[Turk]

If the mechanic did NOT file a mechanic's lien and did NOT establish rightful ownership to this car, the bill of sale you got from someone (whom you can't locate) whom the car did NOT belong at the first place will be meaningless.

When they do a title search, my guess is the car will end up showing as belonging to the original owner.
He may think he does not have any more claims, because rightfully so he probably thinks the mechanic who did all that work transferred ownership.
Once he finds out he didn't, you may have your handful with the original owner.
He doesn't owe you anything, and if his signature is required or a POA has to be secured, you will have a hard time.

Your best bet is to do whatever you have to do, to locate the guy who sold it to you, and have him file a mechanic's lien first and then sell it to you.

TURK