I have repaired my 5th gear problem (it used to keep popping out). This involved replacing the sleeve and the actual 5th gear as well as the components that make up the synchronizer mechanism. It is now extremely smooth - no rattles or vibrations - I think better than when I first bought the car.. I have also noticed that shifting into other gears especially reverse is now much smoother - without that notchy feeling. This could be down to the new gearbox oil that I put in. On a sc