the new oil filter for my 1991 420 SEL came with the rubber gasket for the filter housing and the washer for the top of the housing, it also came with a copper ring (maybe the size of a quarter).

1.) What is that copper ring for (it really is round like a ring not flat like a washer)?

2.) The drain plug did not have a washer on it, is that normal?

usually for oil pan drain plug/bolt

Some filter kits have the extra washer for the position under the spring. I can't remember the SEL setup. I used to change my Mom's but it was a cap only, I believe. If you are able to determine there is a washer at the bottom of the housing spring, you may be able to remove it by twisting the spring to slightly 'uncoil' it and pull outward.

rubber o-ring is for the top. Steel ring (silver) is for the top.

Copper is for the drain plug bolt (small) large copper is for an SL that uses the same filter but a different plug.

__________________
Benzmac:
Donnie Drummonds
ASE CERTIFIED MASTER AUTO TECHNICIAN
MERCEDES SPECIALIST 11 YRS

Ok I took the short bus to school and have no excuse but I forgot/didn't know to put a washer on the drain plug. What should I do.

If it leaks, remove drain plug, install new gasket and reinstall plug then fill with new oil and consider it a cheap lesson. Do not try to tighten it till the leak stops without a gasket.

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Jim