I am about to change the oil in my 1984 diesel and transmission. The shop manual calls for CB or CC grade 30 or 40 weight with a recommendation of Shell Rotella or Mobil Delvac. With CB and CC being obsolete, I am concerned about what oil to use. I assume that the newer oils would be fine but figured I'd check first. The transmission calls for CC grade 20W30 which I have been unable to locate. Is diesel oil or regular gasoline engine oil used in the transmission? What would be a readily available oil to use, Thank you !