I checked my rear diff fluid a few weeks ago and it was pretty low. I could not see any wetness on the axle, so I filled it up and kept an eye on it.
I drove the car for about a week not noticing any leaks. Then one day when it was parked on a hill it leaked out a puddle of gear oil. I jacked the car up and it looks like it was coming from the fill cap, the cover gasket and rear driveshaft seal looked dry. I checked the gear oil level and it was still full...

So i thought maybe I overfilled it. I drove it for about another week not noticing any leakage, then last night I see another puddle under my diff, and my car is parked on the hill again...

I Jacked it up again, it only looks like it coming from the fill cap and the oil level is still fine.

Any thoughts/advice?
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What "fill cap"? The diff is filled via a hole filled by a pipe plug on the passenger side of the housing, just above the axle tube. The lube should be filled to the bottom of that hole. When the pipe plug goes back in, there's no way it should leak.

 

provide pic of 'fill cap' !

 

I filled the diff through the hole in the top where the vent cap sits. Was i supposed to fill it to the pipe plug on the side? If so then that means I overfilled it, probably by a lot.
I did notice my rear diff was much quieter after filling it through the top.
Would this hurt anything?
Should i pull off the side plug and let it drain?

Thanks.

 

Yeah, it is only supposed to be at the level of the plug when it is out (on level surface). The plug is where you fill it.