ORIGINAL: Marcol
You shouldn't use a fuel containing ANY castor oil in a Saito or ,in my opinion, any other engine for that matter.
But Gen Saito specifically states not to use castor oil in the engine. He should know, he makes them !
Here in the US we don't have the super hi-tech synthetic oils that you have in Europe. We have klotz and castor. Castor is what keeps our engines from puking out thier internals and protects them from corrosion.
BTW, I've been running a castor/kltoz synth fuel in my old saito .65 and it's still running on its original bearings after several years of service. The castor turns the muffler brown, other than that, no problems.