D2 Fuel Injector Pumps - Leaking

I've got an issue with the fuel injector pumps on a 1955 Cat D2 leaking, appears like they are leaking around the fuel inlet seal. When we originally got this dozer it wasn't running, had been parked for several years in a garage. You could see that the pumps had been leaking before it was parked. I looked up the parts and pictures in the service books and assumed it was the seal leaking, reasonable thought for a dozer that is almost 60 years old. When we removed each pump the original seals didn't bad, but also didn't look great, and they were 'cone' shaped. The new seal, part number 2A-3307 is a standard looking seal, 0.311" diameter with .188" cross section. I definitely thought new seals would address the leak. Well, we got everything back together and still have the leak. It appears that it's not as bad, but still a decent leak. Has anyone had experience with these pumps leaking and is there another type of seal available? I don't see how a standard seal is getting enough compression to seal because the pump housing is cone shaped and the seal called out is just a standard profile seal. Any help would be appreciated. Thanks, Nate

Use COPPER seals and torque to factory specs.

Not sure we are talking about the same area/location. There are no copper seals in this area, nor do I see how a copper seal would work here. There may be copper seals on the injector, but I'm talking about the 4F-5015 Fuel Pumps, each injector has its own pump and the feed to each pump (low pressure side) is on the back side of the fuel pump body casting. There is a hollow dowel that is pressed into the main pump body and the 2A-3307 seal goes round the dowel. The pump has a cone shape cavity that sits over this dowel and seal. The problem I believe is not enough crush on the seal. If I can find a larger cross section seal that might be my only easy option.

I never see these small pumps leaked by the seal 2a3307

The 2A3307 seal is the correct part number. Did you use Cat parts or aftermarket? Usually don't have a problem with the Cat parts. These are the same seals used on all the early fuel injector pumps.

We used genuine OEM Cat parts. One thing I did notice also when we removed the pumps, there was another smaller profile, larger diameter oring shown in our D2 parts manual. They seal the openings in the main pump housing under each pump, where the plungers pass through to the cam. We installed new ones while we had it apart. Sounds like the 2A3307 oring should work, guess we will have to keep looking for the leak source.