[morzh]

I ran two caps through the dishwasher.
While they did not suffer (not much, anyway) - dishwasher does a number on all my aluminum things, it dulls them - the caps came out somewhat dull and there was, however little, that powdery residue on them.

I actually got better results with soaking in warm water with Ajax dish soap and then the long soft brush.

But the last one, due to no desire to unsolder all that rubber wiring that was still good etc, plus no need to change the grommets, I simply used a can of the duster first, blew all the dust, and then used the Blue Shower cleaner from Techspray. It is clean, shiny, and no water, so nothing to dry up much - the tech cleaner sprays evaporate fairly fast with no need to go in the oven.