[hotmilk400]

not sure what years it is common for, but i know its a problem for 98's. both my ti and my aunts Z3 has/had that problem. the problem is that the track the window slides on is really thin metal, and bends over the years. if you bend the track back, you are fine, but most people/dealers are to lazy to fix it the correct way, and just replace parts (and never fix the bent tracks) .

the window then stays on track for a few more months, but after a few good slams, its off track again. it only really does it if the window is all the way down, since it is barley on the track at that point.

if it doesnt do it after a few slams, it either was fixed, or it never had the problem.

if it does fall off track, its an easy fix. u just need to remove the door panel, and remove the window. bend the track back, and replace the $9 plastic clips if they are broken/worn out. that is really all thats to it, and it might get u some bucks off, or its going to really piss of the guy that u "broke" his window. haha