380SEL Coolant coming from somewhere...

I just had my rad checked out, and I was told that it was holding pressure fine , thus being no leaks. So I had it flushed just for my piece of mind.
My temp guage in dash is still acting weird, although not as bad as before. I was told off this site to clean the rad of bugs - I have done that I have also been told to suspect a faulty thermostat. The only thing I'm wondering is why temp. in dash drops to normal when I crank the heater? Am I looking at a blown heater core? There is also coolant (small amounts) on top of the rad itself and along some of the hoese - which are all tight. If this does sound like a heater core to any experts, what is a ballpark figure of what I'm looking at in way of price from your experiences?
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The car's heater acts like an additional radiator and so, sheds heat from the engine.
You apparently feel the motor is running too hot; it should be about 80 degrees C. with higher readings in slow traffic.
If the motor runs warm at freeway speeds then the radiator is restricted or the coolant flow is constrained. If the motor runs hot in traffic the fans should be checked.
The only other reasons are a bad temp. gauge and / or the engine's ignition timing being too advanced.
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[snip]

A bad gauge would not be likely to fail so predictably as to always read low when the engine is running. And gauges seldom fail, usually it's the sender and usually that is just the multi strand wire failing under work hardening such that it snaps off of the connector.
But, when, not IF the temp and or oil gauge stop working, take the connector off, overhaul it and it'll be literally as good as new.
    http://articles.mbz.org/electric/126connectors /
But, at the age of these cars now any of them with an original rad are probably on thin ice - and rads are prety cheap.
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Radiators for a 380 are cheap and if yours is original I'm not sure I'd even bother thinking about it. Replace the rad and all the hoses.
Flush the whole thing with citric acid. Use new MB coolant. You got evil green stuf in there? They generally don't clog and rust up if you use the correct coolant..
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