Best Automatic OD trans swap for A body car

I'm dropping a 518 off at a guy tomorrow for rebuild. Heard some people say there are probles with them, anyone know what?
I'll tell this guy to fix the problems. Otherwise, it's going to be a stock rebuild with a bolt-in sprag and a TransGo reprogram kit. Going in my Dart, less than 600 miles a year and I don't race it at all. Around town and Highway.