5th gear on my calibra has recently become hard to engage. When stationary, with the cluth fully in, engine on or off, it will not even engage. You can only engage it when driving. Also if you jerk the car hard when it's in 5th, it will jump out. It's a 2.0l 16v Redtop cally with an F20 box. So far I've checked the linkage, which is fine and lined up. There's correct oil and oil level in the gearbox. There's no strange sounds from the gearbox or clutch, all normal. Every other gear engages perfectly. Clutch does not slip, cable adjustment is ok.