ORIGINAL: Red B.
For many years I used castor oil exclusively but have since switched to synthetic lubricants 100%.
For my SAITO engines I have reduced the oil content to 15%. Even though two of the engines have been run for a couple of hundred hours they still look and feel as new when dismantled.
And yes, I do mix my own fuel!
/Red B.
Can I ask what kind of synthetic to you use at 100%, 15% total content? Because about the only thing that has the potential to really be different is the synth lube.