[dsraven]

I have used castrol superclean with great success, wear rubber gloves though cause it could eat the hide off a camel. I usually spray it with a hand bottle pump sprayer, a pump up bottle sprayer or for the big jobs I have a 10L garden sprayer that I have installed a tire valve into the top side so I can simply add 10 lbs pressure and then top it up as needed without having to keep hand pumping it. then rinse the bottle out after if it has any sort of rubber in it. then I head off to the car wash and by the time I get there, like 10 mins, the dirt and crud just washes right off. i don't recommend getting it on any painted surfaces as it will streak them if not rinsed off.
with the axles out I use a wire brush on my drill that fits the axle tubes. you know the kind they sell with a 1/4" shank? I threrad the shank and then use a connector nut and some threaded rod to make a long shank so I can thread the wire brush onto the threaded rod and then use the drill on that long shank to clean thoroghly down the tubes. remove the breather as well so the whole thing gets clean. you could do this again when you get it back so you get all dirt out of the housing before you assemble it. clean any gasket surfaces off before you send it so you know it is ready to go and no extra charges etc. a styro coffee cup works well to block off the axle tubes if needed, not a long term fix but ok for short term.