RE: Saito 125 Fuel Mix
The fuel you described as already having sounds good to me.
It would probably transition a little quicker/cleaner with more nitro, but some have reported that this engine does just fine on 5%. I'd give it a try and find out.
I'm surprised that your importer warns against any castor oil in the fuel. I wouldn't feel comfortable without at least 2 - 3% in the mix. Saito engines do not use bushed connecting rods these days. Plus the castor coats the ball bearings and prevents rust. With just a little castor in the fuel, I doubt if you will ever need to clean the exhaust valve and port.
Ed Cregger