The excessive cylinder wear has to be from a lack of lubrication on those cylinders if the two inner cylinders aren't worn the same. He mentions oil jets, and that they can become clogged. Wonder if the oil jets on those two cylinders were clogged ... he never got into it that far. Plus, he doesn't show the rings on the two inner cylinders that didn't have excessive cylinder wear. I'm not so sure that stuck rings could cause a lack of lubrication between the piston skirts and cylinder ... you'd think it would increase lubrication from lack of oil control on the cylinder walls. But since only 2 of the 4 cylinders exhibited the wear, it has to be a lack of lubrication issue going on IMO.