Well still waiting for the weather to clear, however Celestron sent me this reply about which side of the mount the Dec motor housing should start from:
Celestron write:-
Motor housing should be to the right when facing from the rear. Arrow stickers on the left, pointing at each other.
Bubble level shouldn’t move, should be inset in tripod head. If possible, it is always best to get photos of any physical defects so we can determine it this is a mould over pour or defective mould that need be recast.
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So my new mount was incorrectly labelled and the Dec was around the wrong way! It seems like the fab workers somewhere in China aren't doing basic quality control.