Sounds like you have a Knackered bearing at the top of the steering
Unfortunatly you cannot replace this without stripping the control unit
completely, (i have tried) then the control unit will need setting back
up to work properly.
Your best option will be a replacement, but please dont fit a second
hand one because if the unit has been turned at all since the removal,
the timing of it will be shot and it will be all over the place.
Try Pleiades on 01487 831239 www.pleiades.uk.com