Main Motorcycle: 2016 Thruxton S
Join Date: Apr 2013
Location: Brisbane, Queensland, Australia
Other Motorcycle: 850 Norton Featherbed
Extra Motorcycle: 1960 650 Manxman
Crush washers are soft so they seal better, being a tight arse and not replacing is not a good idea, my Triumph dealer always throw in a new washer when I buy my filters, but in my younger days I would use the old drain plug washers over and over and only replace when they no longer seal and if I had to pay for a new washer what's $1 at the most, you motor is worth a lot more and for the OP 2mm or 3mm as long as it seals won't make much differents at all.