Without seeing pics of the actual machine i cant say if im on the right track.
The old Greenfields i have here (HD8's with the horizontal shaft motors) have two alloy gears that mesh to do the steering. They are awful worn in the 1/2 of the gear that actually does the work. Looking at mine i could rotate each of the two gears 180deg and set it all up with clearance etc and basically be like new.
So i would reccomend, stripping the whole show back to nothing and rebuild the steering. Even if it means removing the engine. Give everything a clean up at the same time. You said that you are sensible, wont take more than that. Greenfields are built around the more farmer end of sensible. Perhaps a little to the right of fencing wire and baling twine, but way left of hydraulics.
