re: How to remove and clean a headlight unit
Just done mine today. Some advice ...
1) Use a large bladed chisel rather than a screwdriver. You need a large blade to avoid chipping the glass.
2) Remove excess caulk from the outside. If you don't it will make it harder to remove the glass, and its' dirty anyway so you don't want it later. There'll be enough spare clean caulk inside that you can redistribute.
3) Don't try and force the whole glass off in one go - the caulk is kind of like Blu-Tack (R) and needs to have time to stretch. First, loosen the grey plastic housing from the glass. Then apply constant force to an area on the top edge until the glass starts to move. When it does, and the caulk goes stringy, use a sharp blade to cut it.
4) DON'T UNDER ANY CIRCUMSTANCES TRY TO CLEAN THE REFLECTORS! They're plastic, and the silvering will have been weakened by the strength of the bulb. If you do see any dirt, just try blowing it. Even the most gentle cloth may remove some silvering (I know, I made this mistake - thankfully not badly).