Phantom wear on nylon strings.

[thankyou]

I have three nylon stringed guitars, a Yamaha classic, a Carvin NS1 solid body, and an old Gibson C1. The wound strings of the first two have dark areas over every fret, and eventually, the windings break, especially on the D (smallest) wound string. At first I thought it was wear, but a friend pointed out that the Gibson doesn't do the same thing. I told him that made sense because if it was wear, it would occur first where I play the most, and I rarely play clear up the neck, where the breakage usually started. He theorized that it could be some kind of corrosive interaction between the frets and the brass. Now, I admit that I don't pay much attention to what strings I've put on them, so I could have coated ones on the Gibson and not the others, but I just don't remember that happening all that often on it - it's my second guitar, and looks a little like Willie Nelson's Trigger and doesn't get played as much.

 

Anyway, I wondered if anybody had any ideas what might cause this string failure. I'm for sure going to replace the bad sets with coated strings to see if that helps.