Convertible window stain issue

Hey guys, I have owned a '95 325ic for about a year now, but unfortunately I'm living out in the desert which means the car goes through nearly
both extremes of weather: 115 degrees in the summer and near or below freezing at night in the winter. The previous owner lived near Los Angeles, so the car had to adjust to its new climate when I bought it. Anyway, just this week I've noticed that the rear convertible window is beginning to get a rusty brown color along the width of the bottom. About 1/16 of an inch so far, but it's notable. I've been trying to take good care of the car (rest of the car still looks great), but because of where I live, that would mean washing it every day to keep it pristine. The car also sits outside all day long--which I realize doesn't help. I've got a cover that I've used when it gets extremely hot, but unfortunately my occupation (reporter) prevents me from covering the car while I'm at work (a part of my job is responding to emergencies as quickly as possible and at that point a car cover slows me down). So, my question is: Is the rust color permanent? What can I use to make sure it doesn't continue to spread (or is the cover the only option)? I just tried a plastic cleaner and polish with the hopes of removing the stain, but had no luck.
Any hints, tips or advice would be appreciated. Mike
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Yes, nothing, and typical.
You can get a new window on eBay though -- cost is in the range of $275. The window is held in with a zipper. When the new window arrives, it should be aparent what you need to do to put it in.

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Well, I guess its time to start shopping. I've noticed the zipper around the window in the past, so I figured it's replacable... I was just hoping for a less expensive option.
Thank you.
Mike
Jeff Strickland wrote:

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