Our RX-8 is a manual transmission; but, I've not heard of any transmission problems. You might try doing a google search to see if you can find trouble reports on this. I did a quick Google search for RX-8 Technical Service Bulletins and only found a couple that dealt with surging at 40-45mph. RX8club has a list of them; but, I wasn't able to get into their site, right now.
If this is a new car, the warranty is a pretty good one and should show up any bugs in the system long before that runs out.
Edit note: I was just reading the other thread that you asked questions in. I see the car in question is a 2004. Listen to the guys in the other thread. Make sure all of the service bulletins have been taken care of. The 2004-2005 series had many problems. It wasn't until 2006 that most of these were sorted out. Our 2006 RX-8 was bought after I felt comfortable that it would be OK. I read Consumer Reports and used that as my guide to buying one, as well. The 2004-2005 vehicles had much worse than average problems. Of course, much has been sorted out, already; but, you need to be aware that the one you're looking at may still have some bugs. I'd certainly want to talk with the previous owner before I'd buy it. The dealership isn't going to tell you its history because it doesn't know, most likely.
