Thanks all.
DMK
Max Magliaro's rebuild guide for the Minitrix K4:
http://www.maxcowonline.com/maxspage/downloads/minitrixK4Overhaul-revision_2.pdf
He does not attempt to optimize contact tracking on the lead (or trailing) truck, but greatly improves the electrical and mechanical pickup from the tender and connection to the motor.
If derailing or guiding, not electrical continuity, is the reason, I'd look into use of tungsten-loaded putty for conformable weight on the truck frame as well as the (relatively long and soft) spring arrangement.
Thanks
Its been a long time, but if I remember correctly you glue an MT coupler spring on the top of the truck so when it is on the track the down force of the compressed spring helps to hold the truck down.
Any ideas as to how to add downforce?