Cerberas

These racks cost a fortune for what they are! Quaife won't deal direct with the public, well not yet anyway! Take the rack out and find an engineering shop that will re-mill the channel out to a larger size then make two new spacers out of silver steel to fit the larger channel and, harden and temper them. You might think hardening is not needed as steel is already harder than alloy but the increased hardness will in fact prevent the spacers from picking up the alloy from the slot edges and then acting as a file between the two surfaces!

I have mentioned servicing steering racks in a previous post and DaveW has an excellent article on how to adjust free play at the rack and pinion gear so a look there would be beneficial. So, two things to do first. If your rack body is secure to the crosshead and the play you have is a rocking movement which can be seen at the inboard (centre) connections of the track rods then this is wear to the slot/spacers and or wear to the pinion gear. Adjust the gear mesh using the rack adjuster as per DaveW's article. The other thing to do and frankly this applies to all owners with a Quaife or jack knight racks, is to lubricate the damn thing! You will find that the rack has the merest smear of grease to the linear rack and to the pinion gear (at the end if the steering column). I have found that making sure your gaiters are sound and functional is vital. When you are satisfied to this end, cut the retaining zip ties to the rubber rack ends (caps) and remove the rubber by pulling it away from the ends of the rack. These are where the rack extends into when greater lock to the steering is applied. I start with the end closest to the pinion gear. Being right hand drive its the right side. I then apply full R/H lock and using a bladder syringe (100ml) I inject about 60-80 ml into the rack aperture. I then fill the rubber end cap with the grease and refit it. Caution here! there is a groove on the rack and a ribbed end on the rubber cap, this is where you fit it, make sure you don't push it on too far as the rack in its travel range will go straight through it! The rack travels into this rubber cap for the full distance!
When all is secure. I then slowly work the rack side to side and with slightly greater turns of the steering wheel to spread the grease into the rack without forming any point pressure until this is achieved. I then repeat this procedure on the left hand side until the rack is fully lubricated and smooth in operation.

Now this is important! The grease I use, and its readily available, is called slumping grease, It is an almost thick liquid grease for use in such things as steering boxes, axle boxes etc. It's designed to be used where movement takes place and is always being redistributed to provide adequate lubrication. A normal grease would displace and sit in areas where movement could not re distribute it! Thus leading to poor lubrication. I have learnt that this is the best way to maintain and service these racks even with some wear to the channel the spacers run in you will notice a huge improvement. I can guarantee that anyone with a car with these racks fitted and with say 3000 miles on the car, go sit in the car and turn the steering from side to side until resistance is felt at the wheel and you will hear the slight knocking noise as the direction is changed. This is the rack gear trying to rotate within the outer tube and the spacers knocking on the slot edges! And they didn't think that would lead to wear!


Potts
You seem to have done good maintenance so far,, just tracking to check to see if that is causing your wandering. again as above an adjustment to the loading on the rack and pinion gear meshing might be in order as per the DaveW article. Its possible that a column UJ has worn but if not again suspect the rack. First though go through all the inspections logically.
With someone in the car rocking the steering side to side slowly start at the track rod ends by the wheel for wear. then to the inboard ends at the rack. are these inboard ends trying to go up and down with a knocking feel or noise indicating wear at the slot/spacer. Check again that movement left and right at about 3/4 lock each side; is it the same or less. the rack slot will wear more in the centre area as this is where most movement occurs through steering input. also don't forget that the steering column has 4 UJ joints along the shaft, one inside the car! check them all. small wear to all can add up and a small rotation of the steering column which feels huge at the steering wheel rim! With someone in the car holding the steering wheel tightly and the front jacked up you can physically try rocking the wheels left and right by hand checking both sides for uniformity too.
Again if the same this points to the rack or column.

Hope all gets sorted for you both!