As much as I love vintage Electro Voice microphones, it seems they went out of their way to make them challenging to disassemble and reassemble.
Don't recall them ever having a "no user repairable parts inside" warning on their stuff.
About 15 years ago I came across a very trashed out RE-20 at work. I sent it back to EV and the cost to totally rebuild it then was $75. That was the original EV in Buchanan, Michigan. It doesn't surprise me that they want a couple hundred dollars to refurb an RE-20 today, though chances are they just send you a new microphone. When mine was rebuilt they returned all the damaged parts.
Life is like a sewer. What you get out of it depends on what you put into it! (Tom Lehrer)