I run mine with R40, both the engine and gearbox.
The old stuff could gel to an extent and certainly would if it came into contact with mineral oil, but the more modern oil seems fine generally if used neat.
Its main attribute is its very clingy nature which protects far better than the newfangled stuff.
I don’t think I like the idea of mixing it with other oils however, I would go for one or the other —

Mike.

Caster all the way for me.
After running model aircraft engines for years without any fault on caster based fuel I changed to modern oils and at the same nitro content. After 1 year I had to replace several bearings and every year after it was the same. I returned to caster based and have not had a failure since. Just ask Roger Moss about his racer when the late Paul Dobbs ran it on modern oils. By the way my bike has little smoke during normal running with Silkolene Casterine.
Wishing Roger the speediest recovery and good health.

There’s no need for fancy or expensive oils. I use the motor factor’s regular two-stroke oil, also no smoke and no problems.