OMD = Oil,mineral,detergent......OEP = Oil,extreme pressure..........I would certainly use the thickest EP oil in the steering box,so it doesnt leak..ie EP 140 if you have it......the diffs ,I would use EP85/140...because S2a diffs need all the help they can get.....gearbox thinner oil,or it will be hard to change gear when very cold............There is one big issue,and that is never use a modern car oil in the engine....use a diesel engine oil........the reason being modern car oils are compatible with pollution devices,and can cause excessive cam and lifter wear.