I have K&N filters among others.
The o-ring is too thin as most of the other filters supplied o-rings.
Only 4mm thick, should be 4.5mm not less.
I bought a 50 pack of ID 89mm, thickness 4.5mm nitrile o-rings from UK.
Think it was here. They have other o-rings needed for the engine rebuild. I bought mostly viton except for this big o-ring.
https://www.ebay.com/itm/133667308715?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=UXpgn1gJSJe&sssrc=4429486&ssuid=XgCEg0CPSya&var=433115506906&widget_ver=artemis&media=COPYThe small o-ring on bolt can be better too.
I tested Viton ID 15 thickness 2.5 mm as used on oil pump and oil lines attachment to CB750 engine.
Tight fit but works fine. Just oil it and oress the bolt in the filter cover. No more oil weep from that place.
I bought a Honda stock big o-ring to compare thickness with, not for use Not cheap. Horrible price when o-rings can be found for a MUCH lower price from o-ring sellers.
The big o-ring will survive at least 2 oil changes. I'll go for 3.....
Do not tighten the oil bolt too hard and compress the o-ring too much.
I did not tighten the caliper much when measured.