CAT D5 injection pump problems/options

Not familiar with your fuel pump, but if the seals are just o rings like the previous style that I have been in, it is no big deal to fix. Just a very good habit to check all the dip sticks on this older stuff every day when you start, so thinning of oil by fuel should show up long before you have a problem. But since I don't know hopefully moving you back to the top gets you more real information.

What's the actual s/n? 1971 is the cross over year from the D333c's to 3306.
I would advise staying with the scroll pump. Cat has gone full circle back to scroll pumps as sleeve metering pumps were not without problems. The old style fuel transfer pump has the upgraded lip type seals over the old packing type. The fuel filter connection to the injection pump fuel gallery is an external connection where any leakage is visible and does not leak to the oil sump. About the only place you could get oil contamination is if you have leakage past the individual pumps which is possible but not very likely and yes, change the transfer pump seals and check the shaft for wear from the seals..

What's the actual s/n? 1971 is the cross over year from the D333c's to 3306.
I would advise staying with the scroll pump. Cat has gone full circle back to scroll pumps as sleeve metering pumps were not without problems. The old style fuel transfer pump has the upgraded lip type seals over the old packing type. The fuel filter connection to the injection pump fuel gallery is an external connection where any leakage is visible and does not leak to the oil sump. About the only place you could get oil contamination is if you have leakage past the individual pumps which is possible but not very likely and yes, change the transfer pump seals and check the shaft for wear from the seals..

todays fuel is what cuases most of these things to start leaking. the ultra low sulphur doest lubricate the same and it also hardens the seals a bit. new seals are more resistant as they tend to use viton rather than nitrile rubber. and any good pump shop can have them done in a few days. when we had the injection pump done for the old mans ute it came back with a new lease of life and used less fuel and it ran better too as it was getting correct fuel load. yes you can modify pumps but its not really worth it as you can create other problems.

Not 100% sure of the year but my serial is 96J2347 both tractor and engine tag.  Makes me feel a little better about my situation.   I've not got the pump apart yet but a previous owner did remove little drain on the bottom of the transfer pump and caped it with a pipe plug so that's definitely one leak issue masked.  

Thank you for helping me out on this.  

Thank you everyone for the input.

At this point I'm committed to rebuilding this mess. Hopefully my engine bearings aren't destroyed by all of this but I'm wondering if I just need a complete overhaul. My oil pressure was good but it started spraying an fuel/oil mix out of the crankcase breather pipe under engine load. I shut it down and realized the oil was more fuel than oil.