Thanks for the response.
We are pretty sure that it is the engine. The transmission has just been upgraded with a Bleazey upgrade and that is now wonderfully smooth.
Car is 2017 and so not an early one. Seems like my initial brief research was right and piston slap does not seem to be common.
Check if there is any play of the Centa with the crankshaft by trying to rock the Centa through the Bleazey access hole. If it rotates, it means your crank-Centa connection is bad and needs a new connector (ie engine out again)...
