Ours has never been in the shop, never a problem at all, but only 110k. The e39 was listed by Consumer Reports (around 2000) as the best car they have ever tested. I don't have much love personally for Consumer Reports, but they do rate things honestly i think. Mechanically it's basically just the same as an e46, but MUCH more space, especially in the back seat.
All that said, find a 530 instead of a 528, it's too heavy without the bigger motor. Also, this one doesn't sound very clean. I've never seen a car missing a sun visor that was properly cared for otherwise. Picky? Yes. You don't want ANY bimmer that hasn't been cared for.
01 330Cic - sold to Mom
02 Dinan 530i - wife's ride
00 323iT - my new toy