Again, mower starts easy and runs smooth. No oil use. No exhaust smoke. The mower originally did require two or three pulls to start before I added a new air filter and a clean plug. But ...
The son apparently tipped the mower on the air filter side, as the filter looked oily and dusty. Oil on the air filter - over fill of the crank case or a tip over?
He must have run it with a partly plugged air filter for some time. Is it also possible the engine internals to be very coked up from a rich mixture? I added a fare amount of Sea Foam product to the fuel, but this treatment may take time to work itself through.
Is it even possible for products of combustion to blow downward through the cylinder rings into the oil? Everyone knows about the opposite, of oil coming up and being burn in the cylinder and making colored exhaust smoke which is not the case.