Thanks Sean
Refreshing my memory on how this goes together, I think the key just spinning may be caused by the tab on the end of the lock barrel not being engaged properly in the rest of the mechanism. Given that this whole thing is mostly lightweight pot-metal it could be that one or more pieces are actually broken, but if that is the case then either the barrel, or the individual tumblers could be swapped in to a used lock mechanism to resolve the problem while keeping the same key.
If anyone wants to remove a spinning lock and send it down for diagnosis / repair then let me know
