Thanks mbdoc,

I pulled the part from the parts car and it does seem that there has been a running change at some point - parts car regulator has
Old MB number 0000781489 (new number listed above 000 078 18 89)
Old Bosch number 0280160512 (new number listed above 0 280 160 587)
Not at all uncommon for updates to parts to occur.

If you search on those they bump you to the newer part. Guessing from the pictures they changed some of the materials, the old one was metal where both the O rings are, the new pictures show blue (one would assume plastic) at the larger dia O ring).

Paul