Sheaffer Imperial IV Seal needed

[Paul-H]

Hi all

I need to find a supplier of the seal that goes between the feed and threaded connector on a Sheaffer Imperial 4

Circled in Red on the attached picture

Anyone know of a supplier, non of my usual suppliers list this part, or is it just a standard o-ring, the one on mine is too mangled to tell what its supposed to be.

Thanks for any help with this

Paul