Gasket part number is 649950  Description in the TCMlink on line parts
catalog:
GSKT-INT.MAN.3.12X O.D.  List price $1.34

PS if you haven't signed up on the TCM site, you can get to the
aviators pages for free and it includes access to parts diagrams.

http://tcmlink.com/aviator/index.cfm

Dan Ballin