Is this like the SM465 where i should use a very specific fluid? gear oil? Any recommendations on weight? I have a 14 bolt On my trailer(might remember an older thread) and I just took my slave axle shafts out of a spare 14 bolt and Im going to cut the shafts off so I can use the ends as covers. I feel bad wasting a good axle.. but i cant find the covers anywhere. The fluid that came out the differential smelled like motor oil and was black. That doesnt remind me of gear lube, at least from what I remember. Anywho, 1) is the end washer/gasket a crush metal washer? Or can I reuse it? RTV? 2) Do I need to flush the fluid and do a cover gasket? If so, recommendations on gasket, rtv, etc. otherwise can I just add fluid once installing my covers? 3) if Im using the differential exclusively for a trailer, should i drain/fill the differential yearly like trailers repacking of bearings, or will it be fine for a while? 4) Is a cover with a drain bolt a good investment? 5) What fluid should I use? EDIT: Im going to use @bucket recommendation of jacking up one side and pouring fluid in. It seems gear lube(what weight?) is the choice?