To test your steering bearings are ok you need to get the front wheel off the ground and very very slowly turn the bars from full lock to full lock, if all is well it will be perfectly smooth if there is problems with the head bearings it will be notchy, its usually most noticable as the bars get totally straight and you can feel a slight glitch in the smoothness, I have had bikes in the past fail MOTS for this reason and when I tested it it felt ok but an MOT tester showed me even a little is a fail in the UK (or at least in his test bay).

Other than this I am at a total loss. Do you have another XT rider near you could meet up woth so you can swap over for a second to check? I have had Distanzias and they are perfect and you should not get this problem at all.