On close investigation, this was suspected to be a leaking pipe somewhere under the floor between the cab desk and engine room. The floors were removed and a small corroded pipe identified in a most awkward location under a partition. The pipe had some complex bends and was taken to a specialist with a 3D scanner and automated equipment to make a new stainless steel copy.
This was fitted a week later to the loco and the floors replaced with new rubber matting. The loco could return to service with a fully functioning straight air brake.
