Complaint / review text:
I bought a used 1999 BMW 323i about a year ago, and last week I experienced the same thing everyone else here has... Got in my car on Monday morning and found that it wouldn't go in reverse. I had it towed to a BMW shop and they quoted me $6000 to replace the transmission. The car has just over 100,000 miles on it, and they're advising me to sell it as-is (not to them, so I don't think they're being dishonest), because in their experience more will go wrong.
I still think I'm going to take their advice, because this is absolutely ridiculous. General advice, though... You'll get a much better price from a transmission shop than a BMW garage. I was quoted $4600 for a rebuilt transmission from the dealer, and approximately $1000 in labor.
Rebuilt transmissions are available on eBay for about $1300, and the transmission shops are quoting between $1600 and $3000 before inspection. I really do like this car, but I've seen nothing so far to be worth the extra cost and hassle of maintaining a German automobile.