I filled a old stuck RD6 engine with used sump oil from the bottom to the very top after plugging any escape holes, it took a fair bit of oil, but not ridiculous, maybe 25 gallons, it was 10 years ago so I can't remember the qty exactly, I got that old oil from my local motorcycle shop, they were glad to get rid of it, the story will be in one of my old threads from 2011 or 2012.

On that engine I'd already filled the 3 cylinders full of 50:50 diesel and ATF down the injector holes for 6 months, but that didn't work, so I figured I had nothing to lose, and it worked a treat, and didn't take long to get some movement.

I could see that tractor had been sitting in a blackberry bush for a long time, it was actually a logging tractor from a wet area here in Oz with a Gas 40 tranny and backend that had been repowered with a RD6 power unit engine, abused to death then parked and left for 50 or 60 years, it had sat so long the blackberry canes had grown through the fins of the radiator!!