As some people here know, I've been friends with, and have done translating and editorial work for, people at Schoeps for over 30 years. Twice during the past three or four years, including this past May when I was in Karlsruhe, I've had lengthy sit-down sessions in which I've disassembled and reassembled capsules under the guidance of their former chief engineer. But even with that "training"--really just an introduction--I would never open any of my own capsules, let alone anyone else's.
The capsules that I took apart couldn't possibly meet factory specs after I put them back together. This is because, in addition to the knowledge, coordination and concentration that's required (and that I don't always have), there are some real trade secrets involved in assembling a Schoeps capsule correctly. I know exactly one such secret--how a tiny marking on one internal part is used for aligning another internal part in order to get the lowest distortion in one particular type of capsule--but I also know that there are others that I don't know about.
Electronic as well as physical/mechanical tests are also done on capsules during assembly. The equipment that they use isn't unique, but the tests that are performed, and when and how they are performed and the expected result values and the allowable tolerances, etc., are never shared outside the company. That's not because the tests are mysterious, but on the contrary--it's because anyone with a physics background would understand all too well if they had those details.
Schoeps isn't alone in this by any means. Today no manufacturer can afford to make it easy for others to reverse-engineer their products. There isn't much mystery left about microphone circuitry; by now, the Schoeps circuit has been copied by any number of Chinese clone manufacturers. That leaves the capsules as the thing that can't be copied, even if all the pieces are imitated precisely.
So, with all due respect to those who may disagree, my honest advice is to send any capsules back to the factory if you think they need work or even just checking and cleaning. I own about 30 Schoeps capsules at this point, and I keep track of when I bought each of them, and cycle them through factory service every 15 years or so--even though I've only had actual repair-type issues with capsules that I've bought second-hand, or the two times when I've dropped a capsule and wanted it to be checked carefully.
--best regards