Did my 1st oil change on my 78 100/7 today. After researching past post on the famous o-ring,I was a little nervous. My canister measured 3.5,I used 1 shim with o-ring and no gasket. The old filter had 1 shim,o-ring and gasket. The hardest part of whole process was getting crash bar out of the way. The search feature on this board really helps out.