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?