do you mean the tuffnol spacer? its a fat brown thing about 1/4" thick that stops heat transfer from head to the carb. its a good idea - I'd want one. available online and the usual suspects.
the sequence should be: head , paper gasket, drip tray, paper gasket, tuffnol , o ring , carb
put heaps of friendly goo on the joins and don't overtighten the mounting nuts as you can easily distort the carb body so that the slide stick open. i use nyloks or consider blue loctite, so it does not need to be tight.
the o-ring can get hard and old - make sure it isn't as can also help distort the carb. some people do away with the o-ring and add goo - whatever makes it gas tight and snug.
