Just changed my Tranny and Primary oils on my FLHTC. The manual says to discard the rubber gasket under the derby cover and purchase a new one from your dealer. Forgot to pick up a new gasket and I had removed the old one so I could wipe the residue from the back of the cover. Went to put the gasket back and it was about an inch too long, would not go back in the groove. Put the gasket in the freezer for a couple of minutes and it fit perfectly. Seems to be doing it's job just fine now.