@Strummer the main problem with the Roco drive is that the pivot points for the gear cassettes were WAY above the frame. This created an enormous moment of torque that causes the whole gear cassette to rotate about the worm wheel, lifting one of the axles off the track! John Armstrong analyzed this phenomenon and described how a couple of brackets could be fitted to stop the truck/cassette assembly from rearing up. Today these are known as "Armstrong brackets." Still, the whole thing was light-duty and half-baked.
There are NO mass-produced diesels in O scale today that have a really good drive.* The Atlas SW comes close, but it's geared like a road engine, and the can motor they used is a cheapie. There isn't a lot of space to replace it with a better motor. Unfortunately, this drive cannot easily be removed and installed in a different loco. So still waiting for a savior...
Tank drives bother me a little, but not as much as Mr. Santiago. Before Weaver/P&D Hobby, All-Nation and CLW used an under floor drive shaft in a robust setup. In HO scale there was Hobbytown of Boston. They even offered a version with a centrifugal clutch between the motor and the gear tower! Running one of these was a hoot. Hearing it rev up and move out slowly with the "prime mover" grinding away was really fun!!
*Clarification: If you consider Sunset 3rd Rail to be "mass-produced," their drive is pretty solid, and has improved with each production run. But it's also a "tank drive" with an underfloor drive shaft connecting the axle gearboxes.
