1990 b2200 rear differential leak

The fill plug is found on the backside of the differential. Remove it, and fill until it starts to drip out the filler. Then reinstall the plug.

Sin - I think he means that he cannot get the fill plug loose.

I'm not sure what a pumpkin is unless it's late October, but when folks have issues with that fill plug, it's usually related to not having the correct tool. The correct wrench size for the differential fill plug is a six-sided 23mm socket; I bought mine at O'Reillys.

Sometimes I miss key info.

I think he was wondering if he instead could use the little hole on top to add gear oil since he was having trouble getting the fill plug loose. He probably could, would be a real hassle; I always suggest getting the right tool and doing stuff like this right.

If his leak was out the axles, that's a tough fix. If from the differential cover: an easier fix; but easier to remove that fill plug THEN remove the rear cover for that.

These diffs have no rear cover. The seal is for the front, which all of the differential bolts to. There is an inner and outer seal for the axles, with a greased taper bearing in between. To remove the axles, you remove the park brake cables, & hydraulic brake lines, remove 4 nuts around drum (they are not attached to studs, but bolts from the inside, which may spin), then pull drum/hub/axle assembly out, the inner seal is right there, bearing and outer seal requires a press to replace. Once you take both axles out, you can unbolt driveshaft, and all bolts holding the front on the differential case, then the pinion, ring gear, and differential come out the front. This is sealed with silicone sealant only.