I changed the location of the screw hole such that, when tightening it, it would lock the inner nut in place on 2 sides instead of 1. This way, it will never rock, but stay locked. I also made the contact area with the inner nut bigger for more stability.
Use the inner nut from the original thing: "Height adjustable router attachment for rotary tool by heron". Note: you might have to sand one of it's corners a bit to fit and also to have a flat surface for the screw. For this base, use 0 horizontal size compensation. For the nut, depending on your 3d printer, you can use -0.10 to -0.20. Better bigger and sand a little. Good luck!
I just tested it and IT WORKS!!! Very precise, zero wobble. Better than the Dremel original plunge base (which is SO unstable...)