It's a long time coming but in case there are still some enquirers...I found that the bulb holder is latched in, the barb type bits are top and bottom in a vertical plane a gentle squeeze and pull is required, right angle long pliers may help, I only found this out after cutting a hole 2"X1" in the black plastic shell across the top of the holder (measured by feel) so that one finger could be pressed down and another, through the provided rear aperture, pressed up, to pull out the holder, no twisting required, the cut out was hot melt glued back, (black sticks are available) it has to be watertight as the headlamp case is a gutter for water from the bonnet.

All this is to avoid removing the front of the car, and all the rusted in fittings involved, to remove the headlamps.

Hope this gives you some better ideas, IF wet does get in, a saved silica gel bag, microwaved to dry. can be stuffed into the unit to very slowly dry it (several days, several bag changes), tie a string onto the corner of the bag so that they can be gently teased out for re micro-ing and replace all the rubber caps at all times.