loud shunt noise from gearbox while driving at approx. 40mph,then lsome loss of power and whirring noise from gearbox.when vehicle stopped with engine turned off the forward gears would not engage until the reverse was engaged first,this seemed to release the brake and forward gear was possible. car moved off in slow laboured fashion. couple of suggestions from scenic owners,This could be torque converter failure/ actual gearbox failure/lack of oil in gearbox. A suggestion an info welcome.