Wildcat Airgauge repair

You can try ACE Hardware in their hardware self serve drawers section and look for a white nylon spacer and cut and file and sand it to fit and trimming it to a hair longer than you think would probably be best since you squash it when tightening for the seal. I think it may fit. Used them for trigger pin shims that I cut and sanded to fit. You may also check the plumbing section too.
 
FX 5003 E14 is your part# BTW

Picture for reference for thickness.

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