On the '05 model you will almost certainly have the earlier reflector based HID lights (check they are factory HID - the headlamp internal surround should be silver not black) in which case the bulbs must be postfixed by the letter R (e.g. D1R) they are physically interchangeable with the S version (intended for projector lights) but optically the "S" ones don't work in reflector headlights. The later projector HID lamps (which are Bi-Xenon) look like the have an egg sized glass ball in them. These take the "S" bulbs.
As has been said, any HID lamp (just like a fluorescent light at home) can deteriorate to a fraction of it's rated output before it fails. Sometimes they also turn "pinky" in light colour.
www.powerbulbs.com has been recommended by a few members for selling genuine, quality branded lamps.