Re: gearbox, uh oh!
If you look under the bonnet , behind the engine you should see the gear linkage coming through the bulkhead (get someone to wiggle the gearstick back and forth in the car while you look if it's not obvious). The linkage coming forward from the gearstick is hooked up to the various levers, etc on the gearbox via a rubber bush which has a metal washer around it. This goes over a balljoint on the gearbox levers.
What happens is that the bush splits and the gearlinkage then comes off the top of the balljoint and you get limited or no gear selection.
Now, IF this is the problem with your car (it may well be something else!!) then there is good and bad news. The good news is that the bits are cheap - actually you just need the buy the washer (I would buy several in case). The bad news is that it is a complete b*****d to do the job. I tried when I had an 8v and gave up. So did one garage I took it to, so go to someone who know what they are doing.
It is possible to do a bodge and just use the rubber bush without the washer, but it probably won't last too long.
Hope that is of some use.