E39-540

Hi, I'm looking to buy a 540 - E39, as I understood there were some problems with the first ones and BMW called them back, could somebody tell me from what year they had to send them back and is there a way to check out if they had the new engine in it, other then the paperwork the owner has. Maybe any BMWwebsites to check the numbers out?
Thanks in advance

This link explains it all.

http://e38.org/nikosil.html