Your seal surface looks to be pitted. If you can't seal that it will get water into it again. I would replace the spindle if possible. If not I would replace the axle. The thing about boat trailers is that they get warm when driving to the boat ramp. Then when you back that warm hub into the water it cools very quickly sucking water into the hub. This is where bearing buddies do their job at keeping water out. They keep pressure on the hub to stop water from being sucked into the hub when backing into the water.