Chaps, I'm doing a bottom end rebuild on my MC21 including replacement of the crank seals. On the parts list diagram there's a thin rubber O-ring listed (item 9 on the pats list, part no. 91301-KV3-771). When I disassembled my engine there was no sign of this o-ring!. Of course, it's possible that it's disintegrated and been spat out of the exhaust but can someone explain where this should be fitted?.