I have the Plantronics PLT V6200 which I bought because of the really long battery life.
Like the other posters here my mic suddenly gave trouble and people couldn't hear me on phone calls .
I tried the Plantronics hub with no joy . I couldn't find the holes to cover because the 6200 has the mic holes at each end of the neck band so I covered the set of holes on the left side of the band (which also has the anc on off button ) and bingo my mic is working perfectly .
Thanks for all the suggestions as I would never have thought of this .