We have seen the same wear on one thruster and the grub screw was loose. This allowed excessive lateral travel. The telltale signs seem to be squealing or excessive lateral movement.
Initially we removed the thrusters to check them all. But after further inspection we learnt it was a simple process to check for excessive travel or lack of travel, and then just remove the rear cap where the power cables attach; locate collar and spin the prop to access the grub screw. The shaft seemed well positioned with about 1mm extending beyond the collar. (Maybe we can get an official measure on that)
We now check prop lateral travel, and added to operational procedures. If more or less travel is noticed, the collar can be accessed easily and adjusted in the field.
After 6+ months, and a fair bit of usage, I expect some grub screws may come loose.
So we advise regular checks be made…
Was going to post a new thread to advise of our experience, but found this already started.