[Shiraz (Ray)]

The rack gears are ground to fit the cylindrical shape of the worm and look pre-worn - could this account for your description of them being very worn? A big issue with these mounts seems to be free play in the worm/gear assemblies and as a first step, you might get a major improvement just by adjusting out the slack in both axes - if you haven't already done it. The worms should mate closely with the gears, leaving only just enough clearance to ensure that they do not bind. I recall seeing a video tutorial on how to do it - should be able to find it with Google. From memory, it involves loosening the two main holding bolts and adjusting the play with the central set screw - then re-tightening.