Could the flex-plate side thrust on the crankshaft be sufficient to actually lock up an engine ? It may be difficult to do at this point but perhaps you could contact the previous owner and ask about any work that may have been completed prior to your purchase.
The symptoms you mentioned (worse case scenario) sounds like the crank or rod bearings may have been replaced without properly verifying the oil clearance on the journals. This is just a guess but - an unknown engine that turns freely when cool but seizes up when hot might be the result of someone’s attempt to mask a low oil pressure problem by installing slightly over sized bearings on a standard crank. The typical lack of oil clearance and lock-up would show up after you had reached operating temperature and the engine was shut down.
Would Ebay get involved in a situation like this and provide some assistance ?
Good Luck, Michael
