Scania Coach Comfort Shift

[bigsimmin]

Hi there, working for a small coach firm. Having problems with an R Reg Scania Vanhool Coach. The vehicle is fitted with comfort shift (very small gearlever, which has air valves at bottom, purpose is to allow ease of driving and select gear before pressing clutch pedal) gearbox. After about 10 mins of being in gear, say travelling along motorway, when you change down or up, say at a roundabout, the gearlever selects neutral but wont select any other gear. Feels as if the lever has jammed at the lever end, but after brute force and ignorance, it will select 3rd. When switched off, the problem isnt at the lever, it moves freely through gears. Has anyone come across this before???
Cheers

[TWR]

Different Vehicle same problem, Scania, Air pipes to the G/Shift full of Muck, remove pipes And blow through also the inlets in the shift itself, there should be 2 small pipes. Problem solved.