I am a frugal read cheap person and in have never replaced that gasket. It has always come apart cleanly when servicing and I just wipe it down and reuse it. there is a nice new one marking the pages used when doing this service in the shop manual

 

LOL, I have service manuals with the covers beat out and used for gaskets, Good Times.

 

I had the original oring on my 07 RG, than moco said they stopped making it and went to print-O-seal paper for a few changes, which I reused the paper (BTW, print to the housing side). Ran across a rubber one, put it in and its been almost 70k miles with the same oring. No leaks

 

JP Cycles