My X300 passed its MOT today
I was a bit concerned as the brakes pump a bit, as if the discs might be slighly warped, but they were fine.
At first it failed because a headlamp was loose and therefore out of alignment. So before I left the garage I had a look and saw that somehow it had popped out of its lowest fixing which is a small ball-in-socket mounting - a bit like a hip joint - which holds it in place while allowing it to move slightly for adjustment. So I pushed the headlamp until it clicked back into place and had it re-tested there and then. It passed with no problems. So that's legal for another year. One less thing to worry about.
I was able to see the relevant fixing by opening the bonnet and looking down behind the lamp assembly while pushing the loose headlamp. I could see the green ball-joint (smaller than a petite pois) wasn't located in the socket, so I just pushed the headlamp in front of the fixing and it clicked back into place with a very satisfying "click". I'm not sure what made the headlamp pop out of its fixing in the first place - perhaps hitting a bad bump or pothole in our 3rd world roads would do it? - but in case any of you X300 owners experience this glitch, I hope this helps you to fix it.