In reply to keith-ratcliffe:
> I have no idea how the mount was damaged - no drops, hits or clumsy fitting, just watch out for plastic mounts.
Fatigue most likely... that's the problem with some plastics.
I'll echo what others have said, whilst I do love the Tokina, it's only suitable for certain shots. I've got landscapes taken at 150mm EFL. It just depends on what shot you are after.
In my kit I've got 11-16 Tokina, 18-55 Canon kit lens (F5.6), 18-135 Canon (F4 i think), 105 mm Sigma (F2.8), Sigma 150-600, all of which have done good "Landscape Pictures" for me