A little more info and couple of piccies...
The long thin plastic panel surrounding the HVAC thumb wheels pops of very easily. I used a flat blade screw driver on the left hand side and applied a little leverage from the adjacent plastic panel. Once the end panel become free it was then simply a case of working around 'unpopping' the whole cover.
Piccy one shows how the illumination is distributed (notice the poor illumination of the right AC control - that's next weekend's job!) Piccy 2 shows the lamp in detail - these just pull out with the aid of thin nose pliers.
However, both my lamps died AFTER I extracted them so I guess they were both 10 years + . However I noticed significantly less discolouration (most bulbs turn black over time) than I expected, but still time for a change.
Piccy 3 shows the headlamp panel removed from the switch behind - and is where my intermittent lamp is housed (top right).
see here for the video..
http://www.mbca.org/northtexas/R129D2-Dash%20removal[1].mpeg
or
1. Using large nose pliers and soft rag grip the headlamp switch and pull. It pops off quite easily.
2. Remove the large nut securing the front panel to the switch mechanism behind.
3. Gently pull and wiggle the front panel outwards.
The headlight adjuster vacuum pipes are quite short so there's minimal movement which makes changing the lamp tricky, so my tip would be to pop the thumb wheel switch out (as shown). You'll see two clips that just need pushing away from the wheel housing one at a time. It came out with ease.
Now the lamp housing is another matter - I have no idea how to remove it! Best wait until the new lamp arrives to see if that holds any clues.