I just removed the convertible boot for some sewing repairs. When I went to unscrew the channeled rail that holds the boot to the seat back, all kinds of screws came out. Some are self tapping sheet metal screws, and some are machine screws. I did see two machine screws that go into the threaded aluminum supports on each side of the center speaker. The rest go blindly into the seat back. Is there any way to know which positions take self tapping screws, and which take machine screws? I don't want to damage an already threaded machine screw hole by driving a sheet metal screw into it. Hopefully someone has been down this road before.