Different types of oil were tested, as shown here, with the hole cut in the top of the casting. Currie specifies a special, extreme-duty oil that they market, which has exceptional properties. The Currie oil has great climbing ability, along with the ability to take extreme pressure and temperature situations. In an emergency, any good-quality hypoid gear oil can be used, but the best oil will make any gearbox last longer. Currie also noted that his diffs require 3 quarts of lube, regardless of the pinion angle or oil fill location and angle.