The item "Engine oil seals, set, Active VIPER" is an engine oil seal set for Active mopeds. Engine oil seals seal the places where the rotating shafts leave the crankcase (crankshaft, gear shift shaft, kick starter) and keep oil from leaking out and air from being drawn in.
Replace them if there are oil streaks on the crankcase, oil is lost, air is drawn in (hunting revs), or whenever the engine is opened up. It is best to replace the old rubber seals all at once as a set.
