Well, the clutch plates are probably in need of replacement. That's about it unless there are any other noticeable issues. I guess your could replace the centrifugal clutch shoes as well but if the bike still bump starts and engine brakes they should be fine.
1985 ATC125M: Parts
1985 ATC200S: 84 200S Bottem end, 200x Head, 200x Carb, S&S Cycle Exhaust, Wiseco 10.25:1 Piston, Reground Cam with About 1mm more lift(unknown specs).
1988 TRX250X
1983 ATC200E: Total Pile.
"Bout Tree Fiddy" Master of Thy 22RE