Cycra rebound problems

Have had a set of rebounds on my bike for a good while now and noticed that they have lost that "spring back" action when you pull them out. I disassembled them last night and made sure the spring was in correctly and put a thin coat of grease on the longer bolts that go through the spring and mount. I've played with how snug the bolt should be and that doesn't affect it either. Short of buying a new pair does anyone have any ideas as to what I could do to fix it? Anyone had similar problems?