Am pleased to say my Pegson Marlow pump is now working well again.
I treated it to some new “snap-lock” couplings, shortened the suction hose to a more manageable length, put fresh grease in the greaser and gave it a couple of turns and then greased the threads on the primer plug on the top.
It emptied the drainage ditch in seconds and was sucking well.
The new snap-lock couplings also make attaching and detaching the hoses an absolute doddle.