the best things i found in FM3 compared to 2 track wise - The return of the point to point tracks, Fujimi Kaido, and the other coastal one..amalfi, i think? so much fun.
most race cars, afaik, use LSD/electronically controlled diffs, not completely locked. As already mentioned, LFS is a litle "flawed" at the moment, as a lot of quick setups (most notably FXR) utilize locked diffs. Do a search, there has been a few interesting discussions on this topic over the years
can't duplicate, sure it isn't something like a police light program, or a sticking "0" key causing your problem? or perhaps the macro program you're using?
Buyer beware. 2nd hand vehicles are always full of the previous owners problems. I usually factor in 10-20% purchase price into repairs before i buy anyway.