Someone on a car forum (who all know I like vacuums) posted up moaning that the turbo head on their dc11 was not turning. Talked him through the troubleshooting and asked about your issue (borrowed your picture too, sorry!) and he said
The wee spring doofer looks like the one that secures the clear plastic shell to the yellow inner part of the bin. Iits across the top of the main removable bit between the two cylinders just below all the whooshy yellow bits, if that makes sense.
Hope this helps!