[Bill Walker]

From my experience, this more likely reflected differences in handling of oil at different units. The actual grade of oil used would be specified for a specific engine type, for a given set of environmental conditions. Visiting aircraft should be serviced in accordance with their specified requirements, or told they can't get that stuff here.

In the civil aircraft world today, one operator might handle oil very carefully, and their crews could take any oil containers, plus any pump, any hose, etc. and be sure of getting clean oil, as per the container labels. At another operator, the crews might know they have to be much more careful in order to get good clean oil, of the right grade, into their aircraft. If you send crews from one operation to another, problems can, and do, arise.