Cheers Dan, appreciate it.
I had to remember the "Never Give Up" attitude today ! I finally got to run the car in the garden, this has highlighted a few issues.
The gearbox has a noise similar to when we used to peg a bit of plastic to the frame of our bikes to flick off the spokes

even though I can't figure out why. Secondly, the diff does slip (not too surprised) but I already had 2 x 0.05mm shims fitted. Lastly, the ESC is acting a bit.. odd ie, car stops dead when I come off the throttle but not always...
So tonight I fitted another 2 shims to the diff & it feels ok, though yet to drive it. I've since noticed another victim of thread lock attacking old plastic, the rear shock tower mount is cracked where the ball studs are screwed in

Luckily I have a spare which I've now fitted.
Anyway, I'll persevere (I have to, I've spent a small fortune on it !)
Retro RC, I saw that chassis fella. I have a brand new chassis spare so I'm counting on not requiring another. Thanks anyway