Axle Shaft Leak

I just had my axles serviced because I had the 8.75 sure grip built with 3.23. While doing so, I had the shop install new axle bearings & seals along with the axle shaft seal. At the same time, I replaced the rear brakes with fresh shoes & hardware. Went to manually adjust my rear brakes today and found the passenger side was leaking diff fluid & ruined the shoes. I went off the road a couple of weeks ago and the car was at an incline where the passenger side was much lower than the driver side. When I originally filled the diff, I filled it to where the fluid was just running out of the filler hole. Wondering if the angle off the road flooded the axle tube and caused the shoes on that side to be contaminated? Some say to only fill the diff to about 1/2" below the filler hole. Don't want to repeat this issue! Thoughts please!