I’d like to also add that as an experienced technician having worked on many Polysix synthesizers, the Tubbutec Modysix is very easy to install.
Also, I agree about the power supply board. I have never seen one that needed any sort of repair and I have been preparing these for near 20 years.
As for the mainboard (CPU board), many of them have the original PCB and are still in good working order. And many of them are still fixable… I have fixed several CPU mainboards and have never had one fail on me. Of course you will still find some CPU mainboards that are beyond repair.