I assume you changed the oil that was diluted with gasoline.
It is possible you have an injector leakdown caused by buildup or varnish that drains them into the cylinder when sitting then leaks past the rings into the crankcase.
If you do have bad spark and the plug does not fire you can flood one or more cylinders and the gas leaks past the rings into the oil also.
What happened to me 2 weeks ago on my 99 Tahoe.....passenger O2 sensor plain quit dead, not lazy but dead. First time I have seen that happen from OK to dead in one drive. It ran full rich as the computer would go (25%). Just driving 30 miles home from work partially melted my headers ceramic coating off. It ran like******at idle.
