Hi MickCooperS,
I've a 04 S and had the exact same problem in sept 05, Lights would intermittently flicker on and off and would have to switch off the lights and then back on.
Problem was the Xenon Bulbs had a cracked Ceramic insulation which was arking (25K Volts
) I had the problem on Both Lights and I Asked the dealer to replace both bulbs and the ballast units- problem sorted
I think it was due to 1 of two things causing the problem
1. Sloppy installation of the bulbs at the factory
2. The Headlights are located on the bonnet and when you open and close the bonnet the force of the lights slamming down cause the cracking on the terminals)
I assume if you've only bought (second hand) the car it's going to have at least 1 year warranty? Bring it back and kick up.
Sharkie