The seal around the throttle lever/speed levers kit is about 20 from Bosch.
The pump to gear housing o-ring is about $5-8 from Cummins, lots of labor to pull the pump to get to the o-ring.
Sometimes the gear housing to vacuum pump area leaks, or the timing pin (timing pin o-ring).
Finally, a bad seal in the vacuum pump will allow oil drip at the coupling between the vac. pump and ps pump/pump reservior.
See archive post for the $40 dollar seals to repair this.
You might also ck. the oil rifle lines that supply the inlet oil on the back side of the injection pump and the supply to the vacuum pump.
It might also be the tappet cover leaking.
Its hard to pinpoint with the fan / road draft blowing everything around.
Try to pinpoint it after cleaning up everything, then maybe we can all help some more.
Simple green works well and doesn't stain the engine paint/compartment. Be careful of letting it dry on warm surfaces though.
Good luck in your leakless quest!
Andy