illegal. WOF time...
Join Date: Mar 2012
Location: New Zealand
Get a torch and look at the place where the driveshaft bolts to the gearbox. You will probably see six hex head bolts sitting 5mm out of the joint - my guess is left side. Grab yourself a 6mm allen head socket, maybe some locktite, and put them back in.
To do it properly, jack the car up, make safe with axle stands, get under it on a creeper, and use a torque wrench.
Then check the other side.
If it isn't these, it could be that the gear lever selector retaining circlip has fallen off. Do as above, inspect the point where the vertical gear lever is pivoted into horizontal movement. If there is unexpected wiggle, pop it back on and replace the circlip.
Check these before dropping the box, the symptoms don't sound like a clutch bearing/actuator lever/pivot pin issue.
Good luck...nice car and thanks for the tip about the earth cable, I'm going to do that to my sprint as the wipers and indicators are rubbish...