just talked to a owner and he's also a mx guy. under part 23(if not there then in poh) he said the plane normal capacity is up to 8 and can be flown to a fifth of that so 4. the engine doesn't need to be overhauled unless there is damage to the rings and such. for the original OP, one quart is not a great situation to be in but as long as no over temp and other engine damage limits have not been exceeded, there is no reason to overhaul. a story i just heard was after doing mx to a eng., the oil wasn't replaced and the mx people started the engine and the engine came to a noisey stop. It ran fine until a minute or so, the engine parts probably started to fuse together which caused the stop.