Well done. The "Oil" that was in it was a 90w Marine oil high viscosity. Some people who used to have motorcycles in the older era used to use that in the rear drive and they just out of habit continue to do so. It won't hurt it but is a definite waste of money. You just need standard 10w30 in these ones.
You don't have to take all the covers off. It is designed to be changed often and easy. Simply remove the fill bolt then the drain plug and let it drain out the old oil then just use a tube extention about 2 and a half inches long to reach in and fill it back up and screw your fill bolt back in.
My gear oil on my genuine buddy never goes bad I recommend changing the factory oil because who knows what that is lol if you have a torque wrench go for it I guess but don’t strip your little gear oil drain bolt for nothing!😂
