I was reading an article on changing wheel bearings. I have a tip for you. Normally, the original bearing is the type you have to pack with grease and seal to keep out the road much. This is usually aging and, probably, leaking. Of course, we all go mad with the pressure-washer, and water gets into the bearing.
Sometimes, the bearings are type SS (steel seal), which isn't much use to keep out water. When I replace bearings on my motorcycles, I use RS (rubber seal) bearings. Use this type and get a good brand. This type of bearings has its own lip seal, plus the seal you already have on the wheel, so there's far less chance of dirt and water ingress. You just have to make sure the seal it isn't damaged when fitting it.