Not sure if this is the bext place to post - there's so much about these lovely Xenon lamps - but here goes - just some shared thoughts.
First - thanks for a great source of info. Especialy the 'how to' guide with pictures. I've worked on cars for over 40 years and it really helped. Also the link to Allparts - really friendly people and a great source of brand new ballast units at sensible prices.
However - if, like me, one of your eyes goes suddenly dull - it is more than likely the ballast. Xenon bulbs are a bit like fluorescent tubes - they tend to make a drama about dying themselves - sudden death is almost always going to be the ballast, particularly if the bulb makes no attempt to light. Bulb swapping will prove this but beware going near them unless they are truly off and cold (high voltages can hurt) and you'll need a flexible friend to get in to change the bulbs without removing the lamps from the car
Which brings me to the next point - you do not - repeat NOT need to remove the whole bumper assembly from the car to get the lamps out. At least this saves you disconnecting all the power wash hardware. If you proceed as if removing the bumper but only ease out one end from the clips, there is quite enough room to lift out the one lamp you need to. This takes a whole load of time from the job and saves the risk of damaging the bumper while it lays on the ground.
Finally - if replacing the ballast - just buy the cheaper one (nearside I believe) - even from Allparts there is a 40 quid difference - and all you get is a slightly longer cable. If you're replacing the ballast - your old cable should be pefectly OK - so don't pay the extra for somethimg you don't need!
Hope this may help others as much as your site helped me - thanks again.