The PO had broken the shifter handle, so I removed it to replace it without any problems. When I reassembled it, I discovered that when I pushed the top button to shift into gear, the top button would move. I was able to see a small piece of plastic down between the center shifter metal shaft and the outer metal that surrounds it keeping the center core from moving freely. How can I access that region or remove the center portion to dislodge the obstruction? Thanks.