Anyway, for info:
1. Under the strip of trim on which the hasard switch is centered, there are 2 little slots visible. Insert a small flatblade screwdriver into one of these and carefully pull the bottom of the trim out. Don't twist the screwdriver.
2. Do the same on the other side. The trim should now be unclipped from the 3 bottom pressure clips.
3. Your ESP and other button faces may pop off. Mine did. No biggy.
4. Carefully pull the top of the trim out towards you. It's clipped in, and slightly wedged under the dash overhang. I used a screwdriver that I inserted between the buttons and the trim to pull the trim towards me without touching the dash or outside part of the trim. Put the trim to one side.
5. Now you need to extract the switch. It's held in by metal barbs and you need to use quite a lot of force to extract it. I inserted a flatblade screwdriver in the top, and prised it out, using some sturdy foam to stop the screwdriver leverage point damaging the trim. Anyway, it does come out; I was about to remove the headunit to try and compress the barbs, but it popped out in the end.
5. Unplug the connecter and plug it into the new switch. Test it before pushing it back in and reinstalling the trim. I didn't because I assumed that the part would work, but it turns out that these switches are crap and my button is sticky, so I had to prise the trim off again to reposition the switch slightly. It's still sticky, but I don't use hasards very often so I'll live with it for a while. I've got 2 years to decide if I can be bothered to return it
Job done. I wonder what causes these to degrade. Mine started playing up then very quickly deteriorated to having no indicators at all.
For info, the part number is: 4B0 941 509K
