75w-140 gear oil is kinda thick, the bearing clearances, etc. are made for 10w-30 engine oil. Honda MTF didn't exist until about '96 or '97, so that's why the older owner's manuals say engine oil. Honda MTF is compatible with those older trannys, & has some EP additives. (It smells a little like gear oil but the viscosity curves are more like engine oil.)