very generic questions will get very generic answers.
www.bmwe34.net has some useful info regarding common problems
the body style u're talking about is the E34....made from 89ish to 95
they are great cars that u should try to find w/ a 5spd NOT an auto esp
if u decide to get into a 525i
do a google search for nikasil b4 u buy a 530 or a 540
in 96 they didn't make a 5 series and in 97 the new body stlye came out
i love my e34 535i 5spd manual 152000 miles and running strong!