Finally following jim s advice and had a closer look at the sensors. You have to look really, really close but the end of the sensor which sits above the ring gear has tiny grooves worn in them. All of them that have failed. I took a paint pen and painted the end of the sensor, re-installed it and did a couple of complete turns, the paint was scraped right off the sensor. There is really no discernible play in the radial bearing, but there must be enough that the clearance is gone between it and the sensor. Looks like I will be changing out the radial bearing and possibly the whole final drive. Wheel seal is leaking and getting a fair bit of clunking/backlash when changing directions. Hopefully that will fix it !! Thanks all for the help!!