Fx D20 and D34 washers

I have a FX Crown mk2 .22cal.. What are the dimensions of the two washers?

D20 part number 19723-1 plastic washer

D34 part number 11507 rubber/steel washer

I know that you don't have to replace them that often but I would like to have them just in case. I will be ordering o-rings in the very near future.

Also, in the schematic diagram it shows B2 and B3 part number 12045 as being 13.95 x 2.62 NBR 70. I can find 13.94 x 2.62 NBR70 and 13.95 x 2.62 FKM (fluorocarbon elastomer, in brown color). Which would you choose?

Take care, Bernie.