On my 1980 300SD there is a metal washer that goes under the bolt head
on the can type diesel fuel filter.  This bolt goes in from the top,
through the filter housing, and holds the filter on.   This washer
forms part of the seal that keeps the fuel in and seems of the copper
type that should be changed with the filter.   However, I've never
found the correct washer, so I've been reusing the washer, together
with a bit or permatex.

Just ordered online what appeared to be the correct and only part and
what showed up is a rubber o-ring type washer.  This doesn't appear
right to me, as I would think the rubber would get squished too much
when the the bolt is tightened   What are others using and where do
you obtain them?

TIA