I have a Steinberger XL-2 fretless with an unlined phenolic fingerboard. There is some wear under A string especially around the 5th position. It's just enough to cause a noticeable buzzing when I play a D. There doesn't seem to be enough fretboard material to sand it. I am considering applying some type of coating to the board to build it up. I hear crazy glue works well. What is recommended?