It`s engine oil that these IP`s need...15w-40 is o.k.

IMHO the independent oil sump setup is better,because:
-you can change the oil whenever you see fit(piece of cake,a syringe and a small hose to suck the oil from top),you can flush easily the whole sump too...
-the oil`s always fresh and uncontaminated...
-you can easily observe the oil level and make conclusion whether it`s diluted too fast by diesel fuel(defective lift pump or worn elements)
-no fuel dilution of engine oil(tired elements or lift pump plunger)
-no engine oil is introduced to the cylinders and burned(same reason)...
Here are some links:
Injection pump maintenance
A PES4M pump takes usually between 180 and 200mililitres(car on flat surface).
Inspect/change oil every(other) oil change. Maybe an overkill,but makes you feel better...
Good luck!