Well, I modified the rubber boot so the heat sink will screw all the way on. If you look in the center of the heat sink and you see screw threads from the bulb, the heat sink is not all the way on. The rubber boot is too long and stops the heat sink from threading all the way on. By the way, you can 1st screw the heat sink all the way on then put the boot on after the modification cut. If you turn the center of the boot inside out you will see ridges where you can start a cut with a blade. I did mine between the 1st and 2nd ridge. One a clean cut has been established you can pull and the tear will stay within the ridge lines.