If you click on my photo (Reply #4) to see it full size, you will clearly see the orientation of the thermal cut out (TCO) switch as it should be.
In particular, the top of the TCO by the 'O' piece is level with the 'stop' piece of plastic behind it. If you (incorrectly) reverse it, the TCO sits about 4mm higher and stops the reassembly from mating correctly. Also, if you don't have the TCO, the 'stop' bit does the same job. Clearly, the TCO needs to be level with the 'stop' bit to work. And yes, I've micrometered all this.
I know it's more 'obvious' to fit the TCO upside down (it was to me). AND, when the 5 torx screws are back in - flexing the casings - you can't see this 4mm gap since it's hidden behind the wheels.
It looks ok - but it's wrong!!
It took me ages to work this one out!!!!!!!
Hope I have helped someone :)