My adjuster unit did not have those grooves when I did my chain/tensioner at 170,000 miles for the first time. I have an early '06 build GTI, with the PLASTIC rings. Did yours have the metal or plastic rings? I would suspect that the metal rings could possibly make those grooves, but not plastic. The plastic would wear down first. It could also be possible that those grooves were intentionally put there on certain build dates for the adjusters ??? Just a thought.