sounds like you have the same problem I do. Check for play in the telescoping part between the two universal joints at the bottom of the column from inside the car.
I can feel all the play there is at the overlapping crash joint, no play to speak of at the wheels. my other Vectra is different and has about 5mm of play side to side invthe front wheels - that I sure is the rack, but it keeps passing MOTs.
Ian.