Typical problem in karting. By the time you need a rebuild you can’t get the seals. It would help if you measured the bore size. Looks like the old DAP seals from 1990. If your holes have lost their coating seals won’t help it much.
FAA certified jet engine and aircraft technician,
Nicholson Speedway class champion 2001,
Yamaha KT100 Service Center,
41 years karting experience