I am in the same boat as you, having just bought a 4.0 2001 disco II. my sunroof doesnt work either. from previous experience with landrover sunroofs, i recommend forgetting its there. dont try and mess with it, you will think its fixed, then one day you will have it open and it will start to...

could be any of the things described here above. you need to check everything. if the wheels are balanced OK the steering damper likely will need replaced, along with whatever other part (or parts) are worn. last one i did was a track rod end causing it.