The pot doesn't seem to be worn out in the typical sense (it's not crackling), but the sound cuts way down when rocked forward to full volume. The rest of the sweep sounds beautiful, but then the last little bit at the end makes the volume drop. Everything appears tightened and in place. Could the string have slipped over the years? Is the pot being forced past it's "full-on" position? Any suggestions? Should I restring it? THANKS.