Axle Case Corrosion

[les]

As a commercial owner the pursuit of a drivers door is a real challenge as they all appear rotten, this seems a case of the offside taking a hammering, the o/s floor of my present project bears this out. The mystery thickens! The nearest I've got to an answer is that the o/s wheels throw up water along with that of oncoming traffic, but the n/s wheels are acting alone? If you don't drive through puddles!