I just did my transmission service a month or so ago. I'm away from home until the weekend. Have the part numbers at home. There are different parts numbers for the two drain plug washers. One is aluminum and one is copper if I recall. Got both of mine at my dealer. I'd you remind me, I'll give those numbers when I get home. I may have posted them here. Do a search for my user name and transmission.

Len
'99 E300 turbo 101,000 miles