I found the missing valve kicking about in the inlet manifold
It has snapped at the collet groove and looks very much like metal fatigue. A crack started on one side of the groove, and just propagated across the stem until it snapped and then the valve just fell in the cylinder. I've never seen a failure like that before on a production engine. It looks like it was running just fine until this too. The other cylinders on this side are spotless. Very odd.
The engine code is AVP by the way
