Automatic Gear Box Indicator lights

For no apparent reason all the gear box indicator lights (Drive,Sport,Revers,Snow and 1234) will light up. Usually there is no problem but occasionally the gear change is very rough.
As soon as I notice the problem I stop the car switch off the ignition, then restart the car, which then runs normally.
My Citroen main dealer tells me that they cannot say what is causing the problem, but suggest that there may be a problem with a relief valve and to replace the valve will cost £500 problem with no guarantee. If this doesn't work a replacement gear box costing £2000 would be required.
Is this reasonable or can some suggest a solution.