I should hopefully be getting a box and matching diff for my RA, I'm expecting th usual nastiness on the outside and was wanting to clean it up nice before installation.

What products/methods would you recommend, and also is there a good product to use afterwards to prevent future corrosion etc?

 

Autoglym Engine Cleaner, a stiff brush and lots of very hot water is useful if it's bare, followed by a scotchbrite wheel on a grinder once you've got the grease out. I'd then coat the box in Bilt Hamber Dynax UC (Clear) protecting wax. You could either do the same with the diff or coat it in something like Autotek or Upol aerosol stonechip (I've just done quite a few bits on the underside of mine with the Autotek stuff).

If there's any underseal spray on the rear diff then I'd give it a douse with petrol/thinners and a stiff brush before doing any of the above to get you back to a clean surface.