Overheating???? Never heard of a 325ci overheating... Sure the expansion bottle can crack, but there are coolant level sensors which say the level is dropping, and it would be a bit silly to ignore that alright. It's the oil usage I'd more worry about but even BMW recognise 1 litre per 1000 on the engine is normal enough. Just my 2c!!

EDIT: Expansion bottle and oil usage are both common issues on that engine!