My RWS Stirrup pump has just stopped working and I am not sure why

Used it this morning to fill my pcp pistol with no problems at all, had a plinking session in the garden then went to recharge it again just now and it locks up when I get to around 50 bar.Bled the line and tried again but got progressively harder to pump and locked up at 50bar again - couldn't lift the pump lever up or push it down. Felt like a hydraulic lock of air somewhere within the system.

Anyone had any similar issues or can advise what could be wrong?

A Parts diagram would be most welcome if anyone has one for a 2 stage stirrup pump