For me, quick blow job with the air compressor, then a thick painters brush for the more caked on crud, for seriously stubborn crap I take the whole unit apart, remove the transformer and give it a blast with a hose and some anti bacterial cleaner then a few days to dry out. As for faceplates and knobs, I remove the face plate, wash with some Fairy liquid and a sponge or a microfiber, if it's got some stuck on crap or tarnishing I use a scotch brite pad and gently wipe with the grain of the brushed aluminium paying careful attention to the lettering, after I give it a polish with some car polish. Knobs, I just fill a tub with warm sudsy water, fairy liquid and a soft bristle tooth brush to get in any crevasses.