Last night I picked up a Topsider pump/canister oil extractor tool from a local boat supply store. Just like the one in the DIY post. What an awesome way to change oil!

Anyway, have a question. The M-B filter kit comes with 4 rubber o-rings to replace existing ones. I am confused about the largest one. Does it go into the little "void" 4-6mm below the bottom of the oil cap, or is it used as the seal between the plastic oil cap and the metal housing used to screw the oil cap into?

Thanks in advance!
George

'99 C43 AMG
'01 Topsider