from what I recall, the earlier model MC21's didnt' have the oil galley for the right side bearings. Honda introduced this in I think 1993 (could be wrong on the year) and followed this into the MC28 model.

So if your engine case has the oil galley hole, and your pump doesn't have the feeder then your end bearing won't be getting the additional oil.

Now you could be in the situation I was in where I had an early model MC21 (with no hole in the cases) but an MC28 oil pump. Took me a little while to figure out why I was getting oil all over everything. Tried to epoxy the oil pump hole, but ended up simple pulling the system and went with pre-mix.
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Charles Gallant