Never thought about polishing the piston top. Worth a try.
Mufflers. See the round black things next to the front wheels?
Them's mufflers. Believe or not but the exhaust pipe is 6mm. Header pipe is 13mm. My understanding is that the Hungarian Impex muffler is prized for it's 16mm header pipe and 8mm exhaust. All I know is that purchasing and importing an Impex would cost more than I spent on the bikes.