I boight an old '92 Nissan RD620 bus, has 22litre V10 engine and an electronic/pneumatic gearbox which I am completely unfamiliar with. I was driving it home, stopped at an intersection. It went into reverse and wouldn't come out. The gearshifter could be moved around at will. The indicator on the dash said Neutral, but the reverse camera and beeper were stuck on and when I let ho the clutch it would go backwards. I turned off isolator, drained air etc. Tried the manual gear over ride switches, but nothing. I got a mechanic out who took the top of the trans off and tried to flick it into neutral but it wouldnt. A second mechanic took the next layer of gearbox top off and got it into neutral. It is now working. However... why would it jam in a gear? Is there a mechanical fault in the box causing it to stick? If so, how much should it cost to rebuild the shifter?