^ i work for a transmission shop and im going to say your theory is wrong, to a point. I've seen a quite few cases where the wrong or cheap brand oil was used and caused damage. Their is a reason your paying more for quality oil and that reason is research and special additives in the oils. I know of many oils that arent compatible with others and may cause clutch problems. (Clutchs like in rears and transmissions, not belt clutch) Some things like a pressure washer i dont mind running walmart oils but in a machine that cost thousands use the best oil you can reasonably afford. Its cheap insurance. Amsoil is great so if your going to run it in your motor, might as well run it in the trans and rears imo. Next up would be mobil1. You dont have to change it that often so why not go with the best for an extra $20 or so