two personal thoughts regarding this video:
first, I had to deal with a few of those 'black-period' u-87's in Rome and one really curious thing about them (to me) was that sometimes the mics would 'lose it' and become dull and unfocused, even if they had very low hours, like the one my musician friend had which was used for a few demos.
often the back side was duller than the front (I've mentioned this before.. I don't know if it was pure chance or maybe something to do with sending the duds to Italy.. I AM JUST GUESSING).
if the paint on the screws is still intact, this might mean that there MAY have been a tendency for SOME capsules to lose the grip, for some reason..
I wonder if those rings could shrink or deform or change in some way over the years.
Second, the brush I saw mentioned by Neumann as suitable for capsule cleaning with demineralized water I seem to remember was of the camel-hair variety.