"Automatic Gearbox Fault"

Hi

My wife owns a 2004 Peugeot 206 SW 1.6L auto which has started to have transmission problems. When cold the car appears to slip out of gear with a loud thud, over revs and has the sign appear "automatic gear fault." on the dash. She stops the car, switches off the ignition and then restarts however on her journey to work (20kms) it will happen 2-3 times. Once warm the problem appears to get better however she is now driving with little confidence in the vehicle.

I had the transmission fluid replaced (not flushed) professionally in December 2013 but things have got worse. I've been advised by a friend who is a mechanic that I've got major problems with the transmission which will cost around the value of the car to repair, with no guarantee that it won't happen again.

Can anyone give me advice as to what is going on and my options please?

Many thanks

Murray