Well you say it shot fine the first year and then the problem started. First are you using rail lube? If you do not use rail lube and it is dry it acts like a abrasive and can wear out a serving real fast,the string thing that I think you are talking about is the serving. Now one problem I had once when I first replaced my serving was the guy put on the wrong kind. Shot it about a dozen times and it unraveled too. Took it back and he said the other guy put the wrong kind on, replaced it and after that was just fine. Did not know there were different kinds of serving thread. Your latch could be a problem, but is strange that it made it through the first year OK?