Was it "gearbox" specialist an "automatic transmission" specialist ? Manual and Auto boxes are as different as chalk and cheese. I cannot see an good Auto-Tran specialist not being able to find a fault after two weeks. In most cases I would always change the fluid as it can work wonders. I am not familiar with the transmission on the Galaxy, but as a rule the fluid should be a nice clear red colour, like wine. If it is brown or cloudy you should change and flush it, even if there are no problems with the transmission.