Pre-war motor racing will forever be associated with the scent of Castrol-R engine oil, mingled with the fuel fumes of those times. Burnt ‘R’ is intended, of course, and it wasn’t only Castrol who made this castor oil-based lubricant.
It would be interesting to know how many other brands there were, and under what symbols they advertised. But Castrol was first, and no doubt this oil aided many rotary aero-engines to function satisfactorily during the First World War.
Incidentally, how nice that Castrol have again made available exact replicas of their old pouring jugs, a set of which, in three sizes, costs £26.75 with VAT and postage. Just the thing for brightening up the vintage or classic-car garage!