D4 7u

The pump will only go on one way. The drive tang is offset.

So if you remove it and don't turn it, it should go back on correctly. If you do turn it, make sure you get the offset correct.

The usual culprit is the o-ring on the ferrule between the fuel filter tower and the injection pump housing. It usually looks like it's some kind of V-shaped packing, but it started out as a round o-ring and that's what you need to replace it with. You'll also want a new gasket for the joint there as well as REALLY LONG FINGERS to get to some of the nuts on the back side of that pump housing😆

Only other thing I can think of that might do that is if your tell-tale lines from the transfer pump and injection pump housing are crimped off or plugged up and the drips are finding their way into the oil pan instead of out onto the ground where you can see them.

yes its a common enough problem apparently.
i had to do it on my 6u

have a search on the forums as this has surfaced a couple of times in the last 6 months.
pulling off the govener helps with 2 things.
firstly it helps you get to the back of the injector pump to undo the 3 mongrel studs
and secondly its a bloody heavy to lift leaning over tracks lifting the whole pump off so removing the govener makes it a tad lighter.
make sure you order at least the following

1 x 4F5418 GASKET
1 X 4B4865 SEAL
2 X 8B4967 SEAL (the orings that are usually the culprits.. one at the front and one at the back of the fuel passage in the injector pump)
1 x 4f3367 - gasket for Goveneror if your going to remove it.
this is all from a 6u manual so if youve got your own or somebody can confirm this i would appreciate it.

remember that the bottom of the injector pump uses its own oil. dont forget to re fill it.
infact checking it might give you a hint to let you know if thats where the diesel is getting into the motor through.

Here is a picture of the seals and gaskets required... the fuel injection pump assembly and govenor together weigh 80 pounds... best to utilize an overhead lifting device if you can because lifting that much while bending over the track is tough.