HEUI, which was developed by Caterpillar in 1993, does use oil to drive the injectors, but it uses only engine oil pressure to accomplish that. The injector itself is still lubed only by fuel on the high pressure output side, and the oil is not exposed to any extraordinarily high shearing effects as a result. The D-6278 test runs oil through the high pressure, fuel circuit side of the injector in the same manner that fuel is delivered by one, and there's a tremendous difference between the 2500 PSI opening and slamming shut of that side of the injector and the 60-80 psi delivered by the oil pump. If your clutch slips with either of the oils you mentioned, it has a correctable problem not related to the oil. That's also a fact.