Anyone who has worked on a C5 headlamp for any reason knows what a pain it is to access anything in that area. Here is a method I use after many trial and error attempts to remove or access the H/L assembly.
1 Start by manually cranking the H/L to full up position than back off a little to relieve the tension on the linkage.
2 Remove the two small bolts & nuts that are at the top and rear of the H/L assembly (these are on very tight so use a good torx screwdriver tip, a cheap one will break). this will allow you to rotate the H/L assembly forward and have easy access to the nut holding the linkage to the motor.
3 At this point it is easy to access H/L bulbs, the five H/L assembly body mount nuts & bolts, the linkage to the H/L motor nut, and the three bolts that attach the H/L motor to the H/L assembly frame.
H/L actuator motor gear replacement on late model C5 requires the prying off of the plastic side cover and than gluing it back on. Sometime the glue holds and sometimes it doesn’t. If the cover pops off later unnoticed, your going to have a problem at the most inconvient time. What is needed in addition to the glue is a mechanical attachment. What I did was to use three flat plain washers ¼” x 1 ¼” dia. (one for each attachment bolt) Put the washer in a vise and clamp just above the center hole. Now take a hammer and tap the protruding part of the washer to bend it about 30 degrees. The bend in the washer should be just enough to overlap the side cover and apply some hold down pressure to the cover when the bolts are tightened. (Note: too much of an angle may damage the cover when the bolts are tightened, not enough angle will not keep the cover on snug).
Chuck

 

Thanks for the excellent DIY, Chuck. Did you have to replace the drive gear or were you replacing the bulbs?

 

Actually, this time, I was in the process of manualy rotating the motor gear 180 deg. with out removing anything. After three failed attempts I decided to remove the motor, look inside, and rotate the gear myself. This way I could be sure that the striped teeth of the gear always rotated away from the worm gear of the motor. I've decided that in the future any work to be done to the H/L assembly will be done on the bench. This way I do a better job and save my knuckles.
Chuck