Everything
Head gasket blew 80000km, A/c compressor 90000km, front wheel bearings 100000km, right power window, thermostat, a pain to change, main break cylinder, too many problems...Everything is poorly made
I will never buy another GM ever again...sad, because I had a Pontiac Transport before this and at 315000km- (had an accident) haven't had 1/4 of the problems that I had with Montana at 150000km.
My right power window also went out - I wonder what it took to fix this one -- new motor, switch, etc.