[Mikeyx]

When using the kick-start, coolant actually squirts from the right-hand-side seam between the cylinder and block. Based on its red color, it is definitely coolant and not water. At least the accessible bolt is tight.

Out of the spark plug hole, the quantity is such that while holding the plug on the head to check the spark, my hand becomes wet. So, quite a lot...

When viewing through the oil inspection hole, oil level is unchanged and color is dark and not milky. So I'd guess that the coolant has not seeped through the crankshaft seals.

Anyway, I will have to remove the cylinder. How much (and how) do I have to disassemble the power valve mechanism? That thingy is something I've never ever touched before.... Does it require more than just disengaging the lever coming up from the clutch side casing?