Argus Cintar 50mm f3.5 Uncoated Lens

I CLA'd a Argus C-2 with a Cintar 50mm f3.5 lens.... The inside of the lens is different in rear than the coated ones I have seen, being that the uncoated one has a cork spacer/gasket under the retainer for the rear element.... Which disintegrated on removal..... Anyone know any replacement solutions????

Check arts & crafts stores. I found one selling sheets 1 mm thick.