The nipple on the drivers side expansion tank flat valve has broken off in the line (the things you find when crawling around under your van).  The float valve is available from several sources, but I see no mention of the rubber gasket/grommet/boot in which it sits.  The one on my tank feels old and brittle enough that it may not survive replacing the valve.  

Does this gasket come with the valve or is there a separate part number I can hunt down?

Roy