auto 300tdi gearbox issue

Hi guys I new to the forum but look forward to reading a lot of posts on here as there seems to be a bucket full of info, I own a 98 300 tdi es but at the moment it has a problem when I put it into neutral, basically if I select neutral the car goes into reverse. I have googled the problem and about 3 weeks ago I found a post somewhere that says the problem could be an o ring on the gear selector but do you think I can find it again so I was just wondering if any body else has had this problem or knows how to fix it?.