2015 Subaru Forester Slow Tire Leak

Hello All,
Wondering if anyone can help me out regarding a slow tire air leak I've been experiencing for the past month or so on the rear driver's side tire of my 2015
Subaru Forester. I began to notice it when the low pressure light would come on, and by trial and error (aka filling one tire at a time and driving around to see if it made the sensor shut off) I determined it was the rear driver's side tire. The low pressure light would come on about every 3-4 days when it would lose approximately 5 psi (went from the recommended 29psi fill to around 24psi). A friend and I looked at it and saw no visible holes in the tire. Since the low pressure light would go off when I refilled the tire every time, I'm assuming it's not a TPMS problem. My friend then recommended that we replace the valve stem core, and that's what we did. After the valve stem core replacement, the tire still loses air pressure, but it goes from needing to be inflated every 3-4 days, to now lasting a week (7 whole days) between refills. I made a tentative appointment with the dealership to get it checked out because I'm getting a little concerned that letting this go for so long might compromise the tire in some way, and I don't want to be negligent, but I'm second-guessing myself.
Since the replacement of the valve stem core, the time between refills got longer, so it seems to make sense that the problem has something to do with the valve stem. Thinking back, I remember my friend loosened it and tightened it (he wanted to make sure he didn't overtighten the new core) when he did the replacement, so I'm wondering if it simply needs to be tightened a little bit? Again, I do want to take care of this problem, but I also don't want to spend what will most likely be a couple hundred dollars at the dealership if I can avoid it.
Does anyone have any experience with this kind of thing? Am I most likely correct in thinking it's still a valve stem issue, or are there other likely possibilties (barring a tiny pinhole leak in the tire that I'm unable to see with the naked eye, of course)? Thanks for any advice!
- LD
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On 7/11/17 7:18 PM, LD1988 wrote:

And the reason you don't just take it to the local tire shop is....
--
My favorite bar has a sign hangin' over the urinal that says, "Don't eat
the big white mint”.
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replying to Wade Garrett, LD1988 wrote: Because I want to try to fix the problem myself first. To use your turn of phrase: The problem with that is...? I'm just looking for some friendly advice here, thanks.
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On 7/11/17 10:18 PM, LD1988 wrote:

Because: It's a hump to do; requires specialized equipment to properly diagnose; requires pro equipment if the bead needs to get broken, the tire removed from the rim, reinstalled and re balanced; a new valve stem and/or TPMS device is needed; tire/wheel work is "dirty," unsatisfying, and unrewarding work which is usually dumped off on the lowest skill new guy in a general repair shop; tire shop grunts are usually a click and a half below the quality of regular repair shop grunts; it's very time consuming; and you're probably looking at a max charge of $25 for a half-hour while-you-wait repair at the tire shop.
That's why;-)
But hey, you wanna do all that, knock yourself out!
--
When a true genius appears in the world, you may know him by this
sign....that the dunces are all in confederacy against him.
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On Wed, 12 Jul 2017 02:18:01 GMT, LD1988

Put the wheel in a tub of water and find the bubbles.
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There could be two problems, only one of which involves the valve stem.

Do you have a large washing tub and a water hose? Even easier, how about soap, water, and a spray bottle?
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LD1988 wrote:

If you carefully inspect the tire, including inside the treads to look for nails (they can hide, like wearing off their heads so just the stem is sticking into the tire), have any roads you drive on be repaved with those damn stone chips aka chip-seal?
https://en.wikipedia.org/wiki/Chipseal
https://en.wikipedia.org/wiki/Chipseal#/media/File:Chipseal_surface_close-up_view.jpg
Those stones are sharp. I don't how they pulverize the stuff but I've see it have very sharp chips laid down. Try walking on them with bare feet. Hot sand would be less painful. Instead of using a heavy roller to push the stone chips into the new tar, they use the tires of cars driving on the road.
I've had a stone chip get wedged into the tire inside the tread. Couldn't see it from the outside. Worked its way to inside. Tire had to be removed and a patch applied inside.
http://www.post-gazette.com/news/transportation/2009/06/22/Low-tech-tar-and-chip-road-repairs-rile-drivers/stories/200906220196
"the pinging goes away in a few days". Bullshit! They leave it on the road for weeks. In fact, you end up with "chip drifts" where the chips have been pushed into piles outside where the tires typically traverse. It's a severe hazard for bicylists and motocyclists as the chip dunes are like coarse sand or gravel dunes and can cause a topple.
Just because you cannot see the projectile in your tire doesn't mean there isn't one. Apparently I spun my tires so hard with a V8 and soft compound tires that a bolt got lodged into a tire. Not bolt end first but head end. That's right: the bolt went into the tire head first. I couldn't even see the end of the bolt when inspecting the tire. Saw the head sticking inside when they dismounted the tire from the wheel. I could understand how nails and chips might get skewered into a tire but this was a big bolt and head first.
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On Tuesday, July 11, 2017 at 1:18:02 PM UTC-10, LD1988 wrote:

Mix up a solution of water and dishwashing liquid and brush it on the the valve stem body and nozzle. If that's not leaking, brush in on the rest of the tire including the rim. Inflate the tire to 45 psi first. Happy hunting!
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wrote:

Don't inflate to 45. Not that it's not safe, but at 45 it may very well not leak if it is a bead leak, while it may leak a lot at 35 or less.
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On Wednesday, July 12, 2017 at 11:13:52 AM UTC-10, snipped-for-privacy@snyder.on.ca wrote:

That's a good point. Apply soap solution to check the rim/bead seal. If that's OK, increase the pressure and test the rest of the tire tire.
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On 7/11/2017 7:18 PM, LD1988 wrote:

Or you could've just gotten a tire pressure gauge. They cost maybe only a couple of bucks at the hardware/automotive store for the analog ones, maybe a few bucks more if you get a digital.

I wouldn't call a 3-4 day leak to be a slow leak, that's actually a pretty fast leak. I have a tire that leaks slowly over the course of 1 or 2 months! It used to leak every month, but then I got it fixed, and now it only leaks every 2nd month.

It could've been the valve stem, but it could also have been a poorly fitting bead around the wheel rims. The standard thing to do here is to coat the tire in a soapy water solution, and then watch to see if bubbles start popping up around some part of the tire. If it does, then that's the source of the leak. In my case, that's how we found that it was the rim to bead interface that was leaky.
It's not unlikely that the valve was also slightly loose therefore it improved the leak time by replacing it, but the real source is elsewhere.

I would never take a problem like this to the dealer, as it's too expensive there. I'd go to a local mechanic instead for this.
    Yousuf Khan
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