Hi Bob
last summer my left piston picked up. Its always the left isn't it!
My pistons weren't Hepolites (GPM). I guessed it was a lube issue but a strip down showed all was Ok with lube. But I still went for new pump, pressure relase valve, and oil filter so I could run modern oils. Perhaps the rich running in the early days after rebuild washed oil off cylinder adding to the inherent lubrication issue on ledt cylinder?