It's funny because there is one on the SS and it's a real arse to get it on there! It's quite a tight fit and every time you try to clamp the outer ring down, the bloody thing pops off.
Took me about 6 attempts before I finally got it right.
Dunno - I'm trying to put that one off for a while as yet...
It looks like I might be getting "familiar" with the damn gasket on the SS again as the tank is being painted now as well. Lets hope it's streched a bit over the last month or two!