I have a used (bought used, obviously i use it though) Klippermate. When i string with it the strings slip while tensioning in the circular jaw thing (dont know proper name). I clean it with a shoe lace and isopropyl alcohol and its okay for a while but it starts slipping again way too early than it should. I have to clean it twice or thrice per racket. Why is this happening? Am i doing something wrong? Is there any way to fix this problem? It's annoying to have to do this when the manual only suggests cleaning that circular jaw thing and clamps once per 5 string jobs.