AJS & Matchless Owners Club

I'm sure this question has been asked before but I have a 1941 350 Matchless G3L ex WD bike and have just had the mag off for refurb.
When removing the magneto drive chain outer cover there is a substantial cork gasket fitted to the joint to retain the grease within the assembly.
The gasket is in need of replacement but I cant find a part number or any mention of it and am now beginning to wonder if its fitted as standard or if its a homemade item.
Any advice would be appreciated.
Many Thanks
BobD

homemade I think, never had one on any of my singles.

I've never seen or used a gasket there and suspect it's a PO's mod, but unnecessary in my experience.