Yep, that's the forward clutch right enough. As grumpy says, the problem is in the centre of the clutch assembly, and it is going to have to come out, to see what's happened; that spring is indeed the most likely culprit.
It's actually many years since I worked on Greenfields; but they have changed so little in their essentials, that the old knowledge still applies. The benefits of having a sound design, and sticking with it!
