RE: What Is After-Run-Oil Made Of?
In practice, I really don't think that it matters that much if you use fuel with castor oil as part of the lube package. Last year I "found" a very old K&B engine in my garage -- it had been there for >30 yrs & it had been put away wet. It was gummed solid with castor goo, so I soaked it in fresh fuel until it would turn over, then I lit the fire & it ran beautifully (even the glo plug worked). After its resurrectional run, I decided to take a peek inside. I had to drill out some of the head-bolt & back-plate screws because the bolt-heads were so corroded that there was no way a tool could turn them. There was lots of castor varnish inside, but no rust.