I tried everyones suggestions but cannot improve things so have ordered a new shifter (R3000) and a barrel adjuster. This is just conjecture so please excuse my lack of knowledge here, but my RD is an XT M772, which was always a bit of a bear to index, but with perseverance it worked well. I was told that a reason it was tricky to index was because of its increased spring tension. Could that stronger spring tension have somehow contributed to the failure of the shifter. its really not that old or abused. Just a wild guess.