Hi, Town Car! I just started driving the '08 Signature Limited (37,500 miles) that I bought 6 months ago, and notice that I have a problem that is somewhat similar to - but different from - Stephan's problem that started this thread. Your link is no longer good, but I did find the tech articles on "98 Onwards TC Exterior Mirror Glass Remove/Replace" and "Replacing Town Car Side Mirror Bolts."
In my case, the problem is that the driver's side mirror sags after being adjusted. It doesn't sag when parked, but does gradually sag when driven.
OK, after driving the car several times a week for a couple of weeks, the problem completely disappeared. I haven't seen it happen in well over a month now. Must have had something to do with the age of the components, combined with having sat for so long without being driven.