RE: Where to get caster oil to add to fuel?
AJ:
High grade castor oil has an indefinite shelf life, as long as it's not contaminated. Back in th old car racing days, driving the small British cars with real castor oil in the engines, we could leave fresh oil in the engine for a long time. The minute you took it out to race the clock started. Turn some fast laps and you had to change the oil within a day or two, else it would congeal and clog the oil passages.
Our model engines don't have that concern.
Bill.