I recently had to replace the cord on my Troy-bilt Tb70SS trimmer. After painstakingly replacing the string, I thought I was done. BUT NOW, the pull string will not retract either all the way or at all when attempting to start. How do I fix this? I called a local fix-it shop and they told me I needed to replace the spring-assist assembly , but on the parts manual I dont see anything called that. Can someone help me