[Nasher]

With the Horizontal piston at BDC to make room for the valves the cam appears to spin over freely enough, with equal resistance to moving the Inlet and Exhaust Valves.
And with the inspection covers off everything appears to move OK, and nothing appears amiss at all.

But, on putting my small Bluetooth Endoscope down the plug hole there is a definite witness mark where the Exhaust valve has touched the piston.

Still feeling lucky I decided to try a compression test using an old set of belts. I'm not sure if they came out of this bike or my M1000DS, but they are perfect to do a compression test without buying a new set of belts.

Unfortunately there is ZERO Compression on the Horizontal Cylinder, compared to a healthy 110psi on the vertical Cylinder.

Being hopeful, it could just be a bent valve, the image from the Endoscope doesn't appear to show any real damage to the top of the piston.

I've soaked the Head nuts, exhaust stud nuts, and those that hold the inlet manifold to the head, in a mixture of Diesel and Acetone, which I'll redo everyday over a few days, then the full extent of the damage will be known when I can get the head off.

I have my M1000 on my lift bench at the moment, and need to finish a couple of jobs on that before being able to get the 1000SS on the lift to make working on it more comfortable.