"With cleaned capsules, it depends on the state and type of soiling, on the expertise, and then on a bit of luck, how good you can get."
That is why I think it was a bad idea for Neumann to publish do-it-yourself-cleaning instructions for capsules. I have seen so many home-cleaned (and now irreparable) capsules, that I strongly advise against trying this. In the U.S. the price of some of Neumann's large capsules is approaching $1000.- At that price, the risk of permanent damage seems too large to try an experiment.
For example, if the capsule is a K87, the pressure relief hole in one of the diaphragms will suck in cleaning water into the inner chamber of the capsule (capillary action). Once the liquid is trapped there, it will remain, until the capsule is dismantled and the two sections are dried properly.
Permanent damage to the capsule results when the conductive gold layer on the diaphragm is scratched or removed by means of scraping solid contaminants (dust, sand) around with the cleaning brush. Especially older diaphragms may suffer from marginal adhesion of the gold, so that even light mechanical pressure can lift the sputtering off the Mylar.
Capsule cleaning is one of the (few) tasks that should be left to a professional.