It could be the trans fluid, but it could be a host of other faults.The gearbox has a lot of relays, sensors, valves, solenoids etc.
You need to get it plugged in to a good quality diagnostics machine and read the fault codes.
Independent garages will be cheaper than Vauxhall dealers but phone around.
It might be worth checking yellow pages for an auto gearbox specialist.
digger
August 2009