As many of you will know, I have accumulated a large number of spare gearboxes and diffs over the last few years most of which are covered in a mixture of oil, road dirt and salt corrosion. Getting rid of the oil and road dirt should be fairly straightforward with gunk or similar degreaser, however, I would like to clean up the general appearance though by removing the surface corrosion and discolouring.
I have tried the wire brush approach including the drill mounted type but this is only partially effective as its difficult to get into all the nooks and crannies around the strengthening ribs on the gearbox/diff casing.
There seems to be a few products on the market which might do the trick: Alu Cure De-Oxidiser which is a 17% phosphoric/hydrochloric acid mix used by the trade. SV-35 PMA Aviation Paint stripper which is a benzyl alcohol based mix of non-embrittling acid and hydrogen peroxide. Another industrial strength alloy paint stripper is AS10 Aircraft Stripper. Fianlly there's RemovALL 520 which is used as a stripper in classic car restorations. The only problem with these are that they are 100% biodegradable and non-carcinogenic. This might seem like a good thing but in my experience to be really effective you really need the nastiest substance known to man which will kill or mutate any known life-forms (and probably the unknown ones from planet Zog too!) then YOU CAN BE REALLY CONFIDENT IT WILL DO THE JOB 100%
My Formula Ford team are currently restoring a '93 Swift and used the last of a very effective alloy cleaner. Unfortunately its now banned which kind of makes my point! 
Seriously though, any suggestions on how to how to effectively clean aluminium castings would be much appreciated. I am excluding media blasting for the time being although I believe its very effective, mainly because I am trying to do as much myself at home rather than sending stuff off to specialists.
. Remedying this effect is a right PITA!
