[Lynn Eades]

With all due respect to your knowledge and experience with tracked vehicles. The point is that, every thing else being the same, tension etc,and the only difference is that one track is more worn than the other, and therefore has one less link than the other side. the machine heads off to one side.
The workshop manual descibes the fault, and how to fix it. By making sure the two tracks have the same number of links each side, and by quarting the two tracks, and swaping the quarters to give equal length tracks.