Hi,
I just wanted to chime in and say that 6-7- years ago when I wouldn't think of opening up a mic ( or any other piece of gear ) I came across three beautiful 451's that were found in a basement. I called AKG and they referred me to a gentleman named Dick Land who lives in or around Nashville, he serviced them and replaced one of the diaphragms for one of the CK1s.
Now I know this is supposed to be DIY, but I remember him being very knowledgeable, helpful and the price was resonable. If you or anyone else is interested, drop an email, I still have his phone #, although I havent used it in a few years.
just tryin to help ;D