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I can't see that oil filter cover sealing very well against the engine case without a gasket. It's metal on metal. But if all the sealing is based off the oRing, then it makes sense. I understand the gasket acting as a spacer too.. but it seems like an additional barrier to prevent leaking.
The parts fiche for a R100CS engine shows that I use the shim, oRing and gasket.
I'll flip them as soon as I am able and re-test.

It's kind of a Catch-22. The o-ring is what does the sealing to the outside, based upon pressure from the cover squeezing the o-ring against the shim. The gasket would only reduce the sealing thus, contributing to the potential external leaking. Not to mention, if the o-ring doesn't seal well, oil will not be forced into the filter, but past the seal back into the sump...internal leaking. So, the o-ring has two effects on sealing. If it allows oil to bypass the filter, that is a long term issue you don't want to deal with. That is why this is called the $2000 o-ring. It probably ranks right up there with a lousy engineering design...the previous /5/6 oil filter arrangement worked just fine...might not have been compatible with oil coolers, thought.

Kurt in S.A.

I agree with Kurt.

The metal shim is to keep the white o-ring from being nicked, cut or roughed up by the end of the oil filter tube, which is inside the engine. That metal cylinder that forms the oil filter "housing" does not have a very fine finish on the surface the o-ring sits against.

I highly suggest you replace the white o-ring just to be safe.

The bike has been out of commission for different reasons but I flipped the washer/oRing around (now seated correctly) and took the bike for a spin around the block today. Prior, that ride would produce a weeping leak from the oil filter cover. Today, everything is dry. Fingers crossed it will hold up on a longer ride and I'm good to go.

jjwithers wrote: ↑Sat Jan 19, 2019 11:02 pm The bike has been out of commission for different reasons but I flipped the washer/oRing around (now seated correctly) and took the bike for a spin around the block today. Prior, that ride would produce a weeping leak from the oil filter cover. Today, everything is dry. Fingers crossed it will hold up on a longer ride and I'm good to go.

In view of all of the above, it might be worth putting a pressure tester on the engine to check the oil is up to pressure... just to give peace of mind.

Rob