When your washers are reduced to a trickle, look in the reservoir at the filter on the bottom of the tube. It pops apart and is invariably blocked with green algae, MGB’s with soft bags suffer worst with algae.
You are nearly an originality freak?
You do this…
Carefully prise open the pump body and insert a plunger type electric switch so the original plunger operates the switch. Wire the unit to a windscreen washer pump and hey presto you have an electric pump system which still looks original from the cockpit.