Drain unblockers

That sounds like a workable idea, although I think I'd need a vice to do it properly. Current workspace is either a g-clamp on a chair or held in hand/under foot on the floor!

I quite like the idea of just chucking it some magic liquid that dissolves all the aluminium but leaves the steel fine and ready to thread into some other cranks!

Look what I found on physics forum http://www.physicsforums.com/archive/index.php/t-105538.html

random internet physics dude I didn't think NaOH dissolved aluminum. We've used it in the past to dissolve hard anodization off of parts and it seems to leave the base metal untouched...

[cite]other random internet physics dude[/cite]It takes a while to dissolve the aluminum, but it does eat it all up. Does nothing to copper, brass or steel though.

[cite]yet another random internet physics dude[/cite] At the beginning, and with a non-hot solution, the reaction is very slow. After the thick layer of aluminum oxide has been removed by the NaOH, the reaction proceeds fast.

Seems like its time to get some sodium hydroxide, a suacepan I don't care about and some rubber gloves!