Sticky Domino Throttle

[trapezeartist]

I've just come across an issue with my Domino throttle. After a small inversion that has left the throttle with a minor scar in the plastic (which may be a red herring), it has become sticky. Off the bike or with the clamp screws loose, it is fine. As soon as I start to tighten the clamp screws the self-closing disappears. I've tried packing the clamps with a thin piece of plastic: no good. I've tried tightening the clamp screws with the throttle off the handlebar and it works fine.

Any ideas? I'm reluctant to take the throttle apart because of the return spring and the alignment of the gears, but that is looking like it will have to be my next move.