Hi Modelman
In answer to your question, the problem is in several areas..
When I joined the track links I used a 1/2 inch by 1 inch nylon spacer for the bushing and used a 1/2 inch aluminum pop rivet in from each side as a track pin..Over time the aluminum rivet eventually loosened and bent under pressure..I still need to replace all the above with 1/8" steel rod..
I made the idlers from RenShape ( a machinable material that is almost like cured Bondo)
I made the sprockets out of a rigid urethane resin and drilled out the sprocket pockets..They are not accurate as they should be ands need to be redone..
The track links are milled out of aluminum and are harder than the sprocket and idlers and have a tendacy to bite in and ride up on the idlers..The idlers should be out of metal..
I do have a couple of videos on utube of the D8 in action
here is one...
http://www.youtube.com/watch?v=M2k68z-t73c
Jerry