Mine have been dismally ineffective since day one unless I use my bar muffs.
So if yours have failed cut them both off and get some adjustable Oxford ones. I've used those on a mate's naked bike and had to turn them down, even in winter !
btw, I tried complaining to BuMW and got a functioning as designed response. Odd really because the loan bike I had out (K1300) worked fine. But did I really expect anything else - no !