Where can I find a "contoured sealing ring?
 

I've got an 85 300SD. Does anyone know where I can get a contoured sealing ring and o ring that seals the lower section of the oil return flow line to the lower oil pan? I'm hoping I don't have to go to Mercedes for this one.

Mine seems to be leaking enough that if I fix it, I may single-handedly reduce our dependence on foreign oil.

Go to Mercedes to buy the part. It is fairly inexpensive and you know you'll be getting the correct one. You may also want to consider replacing your lower drain tube as well. Unless yours is completely clean, there's often rust pitting under the seal that will prevent the new one from sealing as well as it should. I think the total parts cost comes out to about $50-$60.

There are two o-rings: upper and lower. They are both the same. You will also need the flange gasket for the upper tube. You cannot remove the lower tube without also removing the upper.

Do a search in the "Diesel Discussions" to find the complete instructions for how to replace this.

Thanks for the advice, I didn't know that about the lower line. It's a bit of a drive to the Mercedes shop but some things we just can't get anywhere else.