There seems to be a fair amount of wear on the top ring evident in the second from last picture. Also some strange wear on the piston just above the second ring and the second ring has strange looking vertical scratches. The cylinder also shows signs of vertical scratching (debri).
What were you using for air filters?
Maybe a combination of worn rings and then pouring gas down it would wash the oil off the cylinders and reduce ring sealing more.
When the engine was running last did it backfire at all?