I was thinking flywheel too when my problem first surfaced. I have learned that the starters are much more likely to fail than the flywheels. However, I know nothing about your particular car so it is really just a guess. It is probably still worth checking out, even if you are thinking of selling it. A new starter (or whatever it takes to fix things) will make it start perfectly - which is what will impress potential buyers.
1995 E420 - retired
1986 420SEL - retired