As I posted the original question I'll tell all how I solved it: I bought a complete ashtray/cupholder/lighter assembly with the walnut finish already in place. Kinda cheating maybe but I couldn't see any reasonable way of seperating the fascia without it becoming damaged.
The unit I bought was quite dirty and the mechanisms for the cupholder and ashtray were very sticky. I gave the entire unit a good soaking in hot soapy water and scrubbed clean as best I could. Once dried I sprayed copious quantities of WD-40 all over and in it to drive out the remaining water and form an excellent lubricant for the sliders to run on. Since then (touch wood) it has been working perfectly. Jobs a good 'un.