A quick question I have been running an RC10B5 Rear motor and I am seeing significantly more wear on the left had rear wheel bearing. This is the bearing that on the tire side of the rear hub. The bearing's dust cover was pretty much off and worn down to the metal. The bearing still works fine but I want to prevent it from damaging the new one. Any suggestions on cause and fix?

I should mention that where I drive is really dusty with unfortunately a lot of loose dirt. If that is what is causing the wear I would think it would happen on all the bearings but it was just this one.