Most folks use motorcycle oil, some use waste oil. I think there was some benefit for the VE pump engines after low sulfur fuel was introduced in 1993? There were pump failures from lack of adequate sulfur lubrication. I don't think the P7100 or VP pump engines get any benefit at all. VP pumps seem to mostly suffer electronic failures. If you're going to add something think about maybe Motorcraft PM-22-A ULSD Compliant Cetane Booster and Performance Improver. ~ 20 years ago I preferred Mobil Diesel as it seemed to have the highest cetane rating at the time. In recent years I haven't seen any difference in any fuels, so I took to adding the motorcraft product. Seems to run a bit smoother, gains a small amount of mileage, not enough to offset the cost but it's there.

https://www.amazon.com/Genuine-Ford-Compliant-Performance-Improver/dp/B000NUAFH0