If you teach that many students as I do, you sometimes experience things regarding their tackle which require immediate action. I have already met students who had their WF fly line put on the reel by tackle dealers with the wrong end first. Some showed up with far too long tapers (XXD lines) though as beginners they were barely able to hold 8m of fly line in the air when false casting. But what I experienced just recently was unbelieveable.
After a client handed me over his fly rod for a few casts I immediately heard a strange noise when pulling out some line. I asked him about his top guide and if it was ok. He let me know that he did not recognize any destruction of his tackle or parts of it, but as we both checked the top guide we were really more than astonished (see picture). So better ckeck your tackle regularly!
Such extreme notches in the top guide destroy a fly line within a very short time. A regular cleaning of the fly line can prevent it from destroying the top guide, but do not use any aggressive cleansers!