[QUOTE=brittrunyon;870873]I now have a 1981 R 100 & changing the oil for the first time.
I read http://www.largiader.com/tech/filters/ & have come up with this.
The canister depth is 3.1.
It appears to be the squared, not rounded.
So I plan on using a white o-ring with a shim to protect it & no gasket.
This would compress the o-ring by about 25%.
Is my logic flawed? [/QUOT
In looking at Anton's canister chart
it seems to me if your canister depth is 3.1 and you have the sharp (square) edged canister then you should be installing your filter, one shim, the white O Ring, a paper gasket and your cover. In that order.