Hi there,
the problem is actually very simple. Below the battery tray is the input head of the gear linkage, which changes the lateral movement of the gearstick into vertical and sidewards movement for the gearbox. if you get someone to move the gearstick inside the car, side to side, you can see which shaft is moving. That linkage needs to be removed and cleaned and greased. there is a 12 mm nut on the front of the shaft, towards the front of the car.. Remove that and push the shaft out of its housing. It will not come out all the way as there is break pipe behind it. You may need to lever it out of the way to get the shaft all the way out. Once free, it will still be attached to the gearbox, but will be free enough to clean with 1200 grade wet and dry. Then grease and replace. You will find that this will free up your gearshift as good as new.
By the way you will need to remove the battery tray to do this.
All the best
Ravenrigger