[Dukedesmo]

Strange indeed, never seen such a failure before but the good news is that the seal looks fine and a new spring fitted though I doubt it would actually make much difference without a spring? other than maybe on the front cylinder exhaust where the oil pools around the valve.

The (complete) spring is a circle with OD of 12mm, ID 10mm, 1mm thick so call that 11mm overall length, in which case the circumference (C=2pi r) should be 34.56mm and I have 34mm so I'm saying it's all there or at least any remaining fragments are so small that they should get caught in the filter so I can't see it being a problem.