automatic gearbox problem...

[georgio3gr]

A friend of mine just bought an A8 1998' model 4.2 V8... The car was owned by a grandpa and had not been moved for almost 5 years. He changed gearbox oil but it has a problem with it... He selects "D", he starts the car and after a while, as the car moves, the gearbox selects by its own the "N" mode (the gear stick is stable at the "D" selection) and the car is reving without moving... The engineer said that he probably has to change all the gearbox... He found a used gearbox from an audi S8 1999" model but the engineer is only sure that it fits his engine, not sure if it has different gearbox ecu and can or cannot cooperate with his A8 engines' ecu... What do you think?
1) Is the problem he has, a problem with his gearbox or with the gearbox ecu? 2)Does he have to change his gearbox with S8 gearbox and S8 ecu and can it cooperate with A8 engine ecu? If yes does he have to reflash gearbox ecu?
3)What are the differences between A8 and S8 automatic gearboxes?

p.s.: I would appreciate your help... Any exlpanation you want about all above i said, please ask me because i'm not so good with my english. I would also like to add that he connected the car with audi computer but it does not find any problem...

[S4 FoSho]

Unfortunately I cannot help you with your problem. I did, however, want to let you know that your English is quite good for a non-native speaker. In fact, your grammar is better than some people who actually are native English speakers.

[georgio3gr]

Unfortunately I cannot help you with your problem. I did, however, want to let you know that your English is quite good for a non-native speaker. In fact, your grammar is better than some people who actually are native English speakers.

Τhanks a lot... You see it's been a lot of years since i stopped the english lessons so i do my best...

p.s. Your car is very beautiful... I have a dolphin grey non-Sline B7 and i love this colour...

[Scotty@Advanced]

Sorry the S8 gearbox won't work, you will need to find a gearbox with the same code as yours.

[georgio3gr]

Sorry the S8 gearbox won't work, you will need to find a gearbox with the same code as yours.

Thank you very much for the answer...