Which one is the O-ring?
 

in the oil filter shaft there seems to be 2 o-rings?

which one should I replace?

Both. They're the same size O-ring, by the way.

both were hard as rocks. i was beginning to wonder if they were plastic!

so to replace do i just use a pick to pull it out and put new ones in? anything to watch out for?

Yup, just get the old ones off. Make sure the slots are clean before you put the new ones on, and that you have the right size o-ring.

whunter buys the big metric O-ring pack from Harbor Freight for about 3 bucks )(?) and has enough O-rings for all MB applications. Invest and buy, you won't be sorry.

not true.

the same size will work, but the correct size is 7mm for the top ring, and 6mm for the bottom...
both have 2mm wall, so I use 6mm/10 for the bottom, and 7mm/11 for the top groove.

oring kit
 

I just ordered all of the orings (and crush washers) that I need for my 95e300d fuel lines. i also have the Harbor Freight metric kit. I will cross reference using my micrometer and post something. Until I measure for myself, I am not convinced that the Harbor Freight kit contains EXACTLY the sizes required.

Why does the EPC show the same part number for both o-rings?

Do you have a reliable reference for the sizes that you indicated?

They fit.

the pair of 6's the EPC lists, do not fit.
it's stretched too thin on the upper groove.

a pair of 7's leaves the lower groove too large, and the ring gets stuck or tears in the hole.

In my experience, they fit just fine.

He's right, I think. The stem gets wider between them...the 6mm will work for the top one, but it gets stretched out.

As usual VSTECH is right again. They are not exactly the same size.

Define "they."

The o-rings specified by the MB EPC are the same size, even though the grooves are not.

The O rings. If you look at the filter tube, you will actually notice that the shaft gets bigger.

If you look at the EPC, you will actually notice that both o-rings have the same part number. Same part number, same size.