Which cylinder is oil-fouled?

As I said, you are smoking something if you think an incline will cause oil to run up the piston and into the cylinder. You show absolutely zero (0) understanding of how an engine operates. And no, they are not using aluminum tip spark plugs these days, but thanks for the laugh anyway. If you are fouling that rear plug, you have something happening on that cylinder. You could start by checking compression to see what each cylinder reads. Compression may be OK even with rings that are bad as the oil helps seal them. There is a slight chance that you have a weak spark on that cylinder and the plug is gettin gas fouled, but you should also have a warning light for that code. If the plug gets oil fouled again, there are a number of temporary fixes that may by lots of miles yet. I'm glad you have it perked up for now. Next time you will know right where to look.

It's a far more serious situation with transmissions than with sump-fed force-fed Otto engines. SMall gas engines may be more sensitive, and consume oil, since they tend to be splash-lubricated.

YMMV. ;`>