Walbro HD16 Carb Gasket Choices?

[SomeRandomDude]

Im sure this has been asked before but Im not sure what search terms to use. I recently bought a 2010 MS460 and have been stumbling my way through doing a "rebuild" on it (piston, rings, carb kit, misc worn out pieces). When I did the carb the kit I bought had two choices of this gasket, a rubber one and a fiber one. It originally had the fiber. I put the rubber in thinking it was maybe an update or would seal better, but now Im second guessing myself and thinking I should have used the fiber one?

Edit:
I mean the actual black gasket, not the diaphragm behind it in the pic.