My fuel pump went out, filling the crankcase and actually pumping the oil and gas out of my air filter. I think the engine is looser now, and it seems to consume more oil, although I never see blue smoke.
A long time ago, we used to drain oil on my 48 chev, replace the plug, and put a little kerosene into the crankcase and run thr engine for a minute or two and then drain off the sludge that collected,and refill with clean oil, but lots of gas would have to really do things to rings and bearings.
The pump isn't a hard job to change. buy a fuel filter at the same time and change that too.
Mike