[Nonfractal]

On my first attempt I put the motor in the pusher the wrong way and spoilt a brand new Flat 6...any tips on how to eliminate all the play I have introduced into the shaft?!?

I ruined an Avant republic the same way.  
If you have play in the shaft, chances are that you've damaged the commutator or pushed one of the bearings out of its socket. 
You  might take the chance to use this as an opportunity to open a motor and have a look at the damage close up. 
It may be possible to fix it with some washers.
Opening a long can motor requires you to file off the tabs that hold the end bell in place so you'll likely have to glue it back in place 

Alan