I have a FC8600 64". It's about 6 years old. After a pretty large perf cut job our cutter is acting up. It's dragging the knife across when setting up. Also not cutting all the way through any longer. Replaced the cutting strip. No difference. I pulled the cover off the head and found a spring back there which seems to support both the cross cut knife and the cutting knife. Does this need replacing? What else would cause this issue?