It has to do with the engagement dog design on the second gear set. Mine was replaced as well even though I had no problems as was Piggers...I believe he did.
Again, either call Triumph, Newman or your local dealer and have your engine number and VIN (on the headstock) handy. The fix is predecated on engine/VIN number.
Remeber, not all dealers are created equal, some are less apt to be conducive to warranty work than others so you may have to 'shop around'.