As thick as the washer is listed, it must be some sort of foam rubber. If so, it is not surprising that the washer apparently has not survived.
Kent


1937 Chevy 1/2 ton
1942 Chevy 1/2 ton
1947 Diamond T Model 509
1951 Chevy 1/2 ton
1950 Chevy COE Model 5700 ~ "Barney" ~ And more pix