Still no idea:

http://www.mel.lth.se/Publikationer/abstract.htm

 

I think Klingelnberg palloid tooth system means little change to angles of gear teeth. Result is little better force transfer. All gears loose some force in them. GT got latest system so that it gets last bit of hp on the road.

Its also possible GTS box uses same system. No point to stop using it. Just wasn't news anymore in '92 MY and thats why its not mentioned in yearly changes.