Keep in mind most castor oils aren't compatible with race fuels under a certain specific gravity. I know this inclues Sunoco Purple and maybe even c12.

Different brands of castor have different detergents (additives) to improve mixing.  It is up to the individual to test their fuel and oil for solubility at the temperature that they will be using the fuel. 

If you are experiencing mixing problems, a pint to a 1/2 gallon of pump gas in 5 gallons of fuel has always fixed the mixing problems Maxima 927 has had in any race or Av. gas I have used.  Adding 1/2 gallon of pump premium in 4.5 gallons of race gas will reduce the octane less than two octane points.