filler cap
 

Is there meant to be some kind of gasket which goes on the filler cap when bolting it to the tank? or does it just go metal to metal?

No gasket between the outer ring and the tank, no.

Check the parts manuals as it would tell you in there:
http://www.ducati.com/bikes/catalogs.jhtml

thanks antonye.

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.

Bit like the 748/9** fuel pump isn't it Antony, I haven't checked but it does look like the same O-ring

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!