Lucky it was just the diff being a bit loose
It does struggle with the brushless (its only a slow one, but the extra torque makes the gears really work.
I had 3 races with it, and the car handled much better than I thought. One of the rear shocks isnt set up right (its a bit stiff) so the car didnt want to go right
However it still ended up 2nd in all of the 3 heats that it raced in.
I'm going to sort the shock out and I think it could potentially win.
(note it was only a small indoor track, on carpet).