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