I don't have service manuals handy at the moment, but hopefully this will help you out anyway.
These gears are used as a mechanical fuse within these models, they are designed to be the first ones to break in that particular drive train. Tektronix never considered giving these gears seperate part numbers (you have to order a complete fuser tray i believe). However, Xerox designed the print engine of this printer and sold it to Tektronix. The Xerox DC4 (docucolor) uses the same print engine.. and after a while these gears got a spare part number as well.
There should be a white and a black gear (both tend to break after time).. I think they're cold ft1 and ft2 gear. I'm sorry, I don't have the part numbers handy. But if you call Xerox and ask for the part numbers for the ft1 and ft2 gear of the DC4 model.. you should be able to order them. They are exactly the same, but I can't remember which one is the black or white one. Xerox 2nd line Hardware Support will be able to tell you though.