i dont think this old oil idea is correct, just for the sheer fact the restaurant wouldnt be able to produce enough old oil for curries. as curry uses a fair amount of oil and will be the biggest selling item, i cant see how old pakora and bhaji oil would keep up with the demand to keep a uniform product. infact i doubt there would be more than a few deep fat friers of the stuff a week, which would hardly be enough for all the curries they would sell in that time.