A4 97 transmission problem..Please help

I have an Audi A4 1.8 Quatro 97 model. Suddenly one day, it stopped going into reverse gear (automatic transmission). I went to the dealer and he obviously said to replace the trans. It drives fine going forward. Even the milage is not bad (70K). I went to Aamco and they said they have to open it to say anything and it costs 500 bucks to open it. Do you have any ideas? Please suggest...

I don't know but the best place to look for problem like that is here.
http://tech.bentleypublishers.com/forum.jspa?forumID=29&start=0 and do a search