http://i242.photobucket.com/albums/f...el911/FILT.jpg

#20 and #21 are the O-rings.

B- Is the Clean Oil going to the Engine.

C- Is the Clean Oil that has gone through the Bypass section of the Oil filter and is going back to the Oil Pan.

d- I have no idea what passage d goes to.

It looks like if both O-rings go bad there is a chance of the clean pressurized Oil going directly back to the Oil Pan by way of passage C.

Thanks Diesel for posting the Dwg. and the others who had input on this topic. I get the idea that the filter has 2 different filters in one. Sweet! The one at the core is the finest and only filters a small amount of oil that does not go to the bearings.

I see how important these O-rings are now. You folks are very helpful.

I removed old Orings they were brittle. I gained about half a bar pressure at idle. I did not change oil. 1.5 bars before 2.0 bars after. Thanks for assistance.

O'Reilly's has a generic box of o rings which contain that size ... except when I needed them and that part of the box was empty... Do not ask for them by part number or tell them it is for a Mercedes... tell them you want an o ring the size listed above... they were very cheap...

I got 6 from Phil in last order. Cheap.