I'm changing my timing belt which broke on my MM, and I can't find a parts house that correctly identifies the O-ring that is on the tube that goes to the back of the water pump. The tube is in between the two banks of cylinders under the intake manifold.
I bought a kit that included a new pump, cam and crank seals, as well as the water pump gaskets, except that O-ring. It doesn't seem to be a standard diameter, or thickness.

I have looked at Auto Zone, Orielly, Pep Boys, and Rock Auto, they all find some huge o-ring that is not the right one.

Any help identifying what that O-ring part number, or even what I is called, would be helpful.

That is the last part I need to put this thing back together. I'd like to replace it, since you have to take some much apart just to get to it, and the truck has 250K so it is probably due.

Thanks in advance for all the info that is here and the help already given to my previous questions.