05-11-2019, 10:17 AM
The obvious solution would seem to be an insulating shoulder washer, which is perhaps what the original fibre job was. 5/16" is a gnat's off 8mm so perhaps hiding two of these might do the trick without frightening the purists?
https://rover.ebay.com/rover/0/0/0?mpre=...0481731718
https://rover.ebay.com/rover/0/0/0?mpre=...0481731718