I think this is a fairly common problem with relatively elderly versions of the 414, and
is to do with the way the grille is attached to the ring around the top of the mic body.
I've seen mics where it has come completely loose and fallen off -- and was then replaced
backwards which caused no end of confusion!
I'd find a decent mic repairer and have them properly seen to, partly because if you
have it done right you'll maintain the value of the mics (which is not trivial), and
partly because I strongly suspect the RF screening provided by the grille will be
diminished if the earthing around the base has been affected by it being loose and
Technical Editor, Sound On Sound