Thx for all the comments.
To answer some q's:
1. The T/R was inspected by myself before the flight in which this erosion (I agree a more accurately worded description) occurred. At the time of insp, the blade paint was indeed showing signs of being 'rubbed off'; by what exactly I do not know, but no where near to the extent as can be seen in the picture.
2. This ac is not flown in sandy conditions and to the best of my knowledge, not overly exposed to rain where possible.
3. Without checking, I cannot confirm the hours this t/r blade is on.
It's a lesson learnt, thanks again, it's interesting to hear your opinions.
hHJ