Mine went out a year ago, got a quote at $1500-2200. HAHA, yeah right i'll keep the windows down.
Also be sure u get the rails on the sunroof greased often, mine broke due to not enough grease ($600).
There are no other real risks that i can think of...Just of that damn plastic radiator neck that broke yesterday, only $200 i'll live
Have fun with the new/used w124