Congrats on getting the stub off! After that, the rest of the Michell technoweight installation is very easy. I installed mine a few days ago. Nice upgrade
After thinking about it, I believe Rega has no choice in installing the endstub that tightly. Once I got the stock endstub off of my RB301, I screwed it back onto the arm with my fingers while wearing a rubber glove. I tightened it as hard as I could.
I then put back the stock counterweight. As I was twisting/rotating the counterweight on the stub, to put it back to the right spot to adjust the weight, I noticed it was really tight on the stub. Those o-rings in the counterweight stick very tightly to the stub, almost like a clamp. Tight enough, that when I turned the counterweight counter clockwise, it would unscrew the endstub. I tried it 3 times, and each time rotating the counterweight counter clockwise unscrewed the stub; even though I had tightened the stub as much as I could by hand (wearing a rubber glove).
I think that is why Rega puts it on so tight; to avoid the counterweight unscrewing the stub during setup. Imagine all of the complaints Rega would get if this happened!
Of course, the stub does not need to be that tight with the upgrade weights (Groovetracer, Michell, etc), because they slide back and forth on the stub, without friction, to adjust the weight.