Microphone Cleaning

I have a pair of U87s (I bought them new around '70 ish;)
 
They used to sound great recording to analog tape; now into DAWs not so much. (pretty noisy)
 
I have been careful in the upkeep as much as possible; but they have seen better days.
 
Could they need cleaning? Can I tell somehow by sight? (they seem to record 'ok', just a bit 'hissy';
(going through a Grace PreAmp)
 
Any recommendations on sending them out for a 'checkup'.
　
Obrigado

+1^  I don't think I would try to clean them myself, but I would also want someone I trust or that Nueman has a contract with to do it.

Hissy would indicate the electronics need some testing, I would leave it to a true pro and I wouldn't even think about attempting to " clean" the capsule surfaces. Those are very thin film membranes that are fairly precisely tensioned. A good tutorial on how they're build would be to try and google a  " HOW It's MADE" episode involving MIC building. They have an episode specific to how a Neuman u87 is built.

hiss comes from many sources.... most common in the electronics and amplification circuits.

Cleaning a mic, not something I would attempt to do at home. Send it to a factory certified shop.

I have a Shure SM-58 that I have had for decades. It has been on many a stage and put in many hours. Without getting too disgusting... it had to deal with all the breath of all the people that used it and abused it in nightclub settings.... smoke, and alcohol condensation.... and it still works fine. I never really thought about cleaning it. The wind screen yeah, disinfected it actually.... the element.... no.