It may be more than just a seal. Frequently that type of seal only starts to leak when one of the bearings starts to fail, and allows the shaft to move, which ruins the seal. You may get it apart and find that the seal is bad, but you've also got a couple of large bearings that need to be removed/replaced, etc. Frequently they're bigger than what most folks can deal with.
When I had to replace similar bearings on the front axle of my backhoe, the local heavy equipment shop wouldn't even touch them...had me go to a machine shop that specializes in larger parts...$120 and I had it back in 2 hours. I'd guess the rear axle bearings on your RX are at least as big as the front axle bearings on a backhoe....just a thought.
