Good Choice!

Gumming at that percentage is no problem especially when the castor is Benol .

Despite dire warnings to the contrary, I have been running a small percentage (2% to 4%) castor in all of my four stroke engines for several decades. Not about thick, thin, etc. The Extreme Pressure qualities are beneficial to the cam, lifters and gears. At those percentages it seems helpful to ball bearings as well.
No ring gumming valve sticking issues at all. Many engines here with loads of hours running time.


BTW, I have serviced many engines with ball separators failed. Of the cases where oil used could be verified, every single one had been run on 100% synthetic oil.