I have had my 98 528 5 speed for 3 yrs . I had a 92 525 touring for over 10 yrs. i have found the e39 very reliable, similar to my e34 as far as problems, cooling system etc. The biggest problem as discussed is age. These are now old cars. I wanted anE34 540 but the idea of buying a 17 yr old car scares me too much. Not many parts last more then 17 yrs.
A buddy has a shop and he just changed the motor for the 3rd time IN A ROW on a 2003 540. All replacements covered by scrapyard warranty incl labour..so he made money .but the later 540 motors scare me.