If you really like the car, and want to know exactly what is going on with the engine, spend $30 and have the oil tested at Blackstone labs:
https://www.blackstone-labs.com/free-test-kits.php
They will be able to identify any problems in the engine based on what they find in the oil. You get a very detailed report back on what the oil has in it and commentary on what they see going on in the engine based on what was found in the oil.
I'd probably do this just to point out that he was lying to me. But then again, I've been told I'm an a-hole.