Pechmo,
I used to do an average of around 150 km per day and
the only real grief I had with the gearbox was having to replace the clutch brushes on the transmission once. I have had some problems recently, but this is down to the fact that the car has been off the road for a long while now.
The clutch itself is pretty good, but John H is right when he says that problems are expensive to fix when the gearbox screws up.
Check that the gear lever clicks into place when the you select drive, reverse etc.
The light indicating the gear you are in should only light up one of the indicators, if it starts to flick back and forwards(assuming the gearstick is sitting correctly), then you may have a problem with the gear selector cable. (easy to replace, and rarely gives trouble)
The ECU (electronic control unit) rarely screws up ,and I have had no problem with mine
I settled into the habit of checking the gearbox oil every three months, and have only topped it up it twice.
One problem with the Selecta Panda's is that the front brakes are not standard Panda fittings. They are pretty expensive to replace the calipers. I have another two cars which I keep on the road and the Panda fell into neglect. Hence the reason for replacing the calipers, and discs.
Make sure that you run the car on long journeys as much as possible. I drove from my house to Edinburgh on a motorway every working day, and the engine is still running sweetly.
The Haynes manual 0793 covers the selecta models for the Panda up to 1995, so I would recommend it as a useful tool.
let me know if you need any more info
Andy