The button on my shifter, on 2000 Chevy Prism, will not engage the rod housed inside the plastic cover. I removed the cover and have to manually push down on the rod to engage reverse or drive. When I put it in park, I have to manually lift the rod so my car key will come out of the ignition. The rod does not seem to spring up or down anymore. What is going on with it, and how can I fix it myself?