[JaguarXJ220]

Some things just cannot be resisted.
Avant Slot. Having read about the standards I checked before I ran it and... the rear axle had been forced down on to, and had jammed the drive shaft/pinion beneath the crown gear. It was pretty awkward and time consuming to get it positioned correctly. 
Once that was done it runs well, it looks great and it stops really quickly. So quick I don't need to release the throttle until the car is already in the corner.