[dazee]

I may well be looking to get some if this current path does not work out.
The main problem I believe is that there is just so much flex in the rear.  From the side mounting points there is literally nothing securing the the motor or rear wheels apart from the 2 thin strips of chassis that attach to those siide plates.  The whole rear is like a swimming pool diving board how it bounces up and down.  And I think the Pointer 5 motor that it uses is quite strong and makes it bounce around coming on and off throttle.

This is at least my view of it.

My fixing plates are now going on to a 3d printed carrier.  The carrier screws into the original body posts on the car.
The rear Plafit axle carrier that screws into the motor has a couple of cutouts in it so you can access with a screw driver to remove the motor.  In my 3d printed carrier I put in a couple of locating tabs that fit this.  This now puts that rear under a little tension and removes that springboard effect.

Really hope it works....