Just discovered that Cillit Bang is excellent at removing the stuff that leaks out of old batteries.
Found a multimeter that had been in the shed for 10+ years and the batteries had leaked green gunk all over the inside of the battery compartment. One squirt of cillit bang and a gentle scrub with an old toothbrush and it sparkles like new!
Have also used Cillit Bang for removing rust on sheet metal; spray and scrub with fine wire wool and the rust disappears.
sponix