Synthetic is almost a must for heli engines,heli engines run hotter than plank engines,and all the synthetics out there have oils that withstand the heat and wear that heli engines get.
15% CP is fine for your 32,the only way youll ever tell you ran 100% synthetic is how clean the engine will be after youve run a few gallons thru it,w cp 15 youll see a slight green tint from the dye in the fuel,run castor and youll see a lot more than tint.
Planes run good w castor,if thats what they prefer,but like the rest of the gang indicated, castor leaves crud all over the place,but most important, wont take the heat like 100% synthetic fuel will.todays synthetics also have additives to give better lubrication,lubricant adhesion,and anti rust and foaming agents.
Do yourself a big favor,stay away from castor based stuff....