Rotax Seal O-Ring for crankcase. This seal O-ring keeps oil in the crankcase and prevents leaking around the connection bolts.
These O-ring seals are vital for protection of the crankcase. A humble part, it is noted by part 18 on the list.
Each o-ring is sold separately. There are 5 of these around the crankcase. They are M6 x 10mm x 1mm.