BMW metal are not very good.
The old ones had poor rust protection. I've mainly had E30's before and they all rust like crazy if given the chance.
But the rust is also dependent on the climate, largest problem here is all the salt that's poored on the roads during the winter.
Even the new BMW's rust (cheap bad paint), but not as bad as Mercedeses.
<img src='http://www.vovvenviggo.se/ilivetoride/sig8.JPG' border='0' alt='user posted image' />
1994 Arcticsilber M3, 286hp, 18" AC Schnitzer wheels.