A haaaa!
I writhed around in the rear of the car and slithered into the boot this morning, finding that (quiter right limeycharger

)the rod had come away from the barrel.
So to stop it happening again I've taken the barrel out but can now see the original pin that held the rod to the barrel is missing(disitegrated?

) and the spring clip for it has pretty much decomposed too.
I was going to try a small roll pin or a split pin...unless....maybe someone stocks new'uns??