Thanks fechter and all
I've applied transistor the fix to my brand new BBS HD and the throttle is working really well (as good as a pre 2016 BBS02 I have built)
I didn't do anything special and I would say to others reading, the potting is nothing like as bad as i thought.....just get in there.
Perhaps there are different types of potting but I had spent too much time reading and not enough time doing. You can easily easily remove it, cut it, separate it or just generally pick at it with anything blunt. Use all the good photos here to guide you as only a little needs to come off.
I was able to pop the board out of the housing by 'breaking the seal' so to speak after taking the potting off around the edges and prying a little between outer casing and the transistor heat sink. Once the board wiggles even a tiny bit you are there. I had it out in just a minute or so.
Mine had little thermal paste and a lot of the potting had bled into the gap between heat sink and housing. This makes we wonder how much cooling they need? I doubt the potting is a great thermal bridging material.
I modified on the side where the wires are attached to the PCB, connected the throttle wire direct to PCB and by popping the pins out of the PAS connector I was able to splice with heat shrink over them.
Also swapped the shunts and so far so good at 40a :p