It's a lot more likely that your knock point just got messed up over the years. String is probably fine. With a knock high tear you need to lower your knock point or raise your rest, either should take the tear out. Just remember that a little movement in the knock point or rest translates to a lot of movement downrange. A 1in tear is bad but not terrible, you maybe only need to go a 1/16 of an inch, possibly less.