Hey everybody, I just picked up a used AKG C414 B-uls off eBay. It appears to be in great condition. I am digging the sound and I am planning on replacing the electrolytic caps with films. However, upon taking it apart, I noticed a spot on the capsule that looks like it is rubbing off. This is my first time working on a mic as far as upgrading components on a circuit so I am admitting ignorance. Could someone tell me what exactly has rubbed off here and is this an issue going forward? I don't notice any sound problems. I took a picture of it for everyone to reference. Thanks for any help here.