piston rings
Is the engine burning oil? Do you have the drool tubehead? If you arent using oil and have a drool tube around the plug, you may be fine.
If not, I still agree with making certain the rings are the source of the oilfouled plugs. I would do a cylinder compression test and a leak down test first and make sure it isn't valve seals, which would be a far easier fix. It you do have to replace the rings, you should consider some other work to do while the engine is dismantled.