I don't know the internals of the 1219, but from my experience working on other Duals, I'll tell you this... If you open that puppy up and start tinkering, be careful and draw diagrams. The mechanisms on those things sometimes consist of overly-elaborate systems of levers, springs, cogs, and the like.
I know the 1219's were indeed an idler wheel configuration with a 4-point gimbal tone arm. It's a good idea to keep that idler wheel clean to avoid Wow & Flutter issues, and to not introduce any additional rumble. I don't think the rumble on these things was bad at all to begin with.
You should throw up some pictures.