We replace a piston when it is worn, symptoms of oil consumption and often a blue smoke from the muffler.
It is caused not by the seals valve but by a defective air filter. The dust enter into the engine and do like a grinding paste between cylinder and rings.
Usually the rings worn first. You can control by placed only the ring into the cylinder so as to check the clearance between the ends : 0.5mm max.
The cylinder, much harder than the piston, less wear.
The clearance between piston and cylinder is measured in the lowest part of the piston : correct 0.03/0.05mm max 0.10
0.05 is the thickness of a sheet of cigarette paper
The bright ring (steel) is above
The black one ring (iron) is second