I finished my Auto-RX treatment around 10K miles ago. My 1997 Monte Carlo LS has 175K miles on it now, I originally used it because the engine began to sound a little on the rough side (it has always had piston slap, but the valves started to sound unpleasant) and it would burn oil when it was cold or if I went full-throttle (often).
Well, the oil burning slowed way down, I really don't even notice it burning any oil now. I used to get a big 'ol puff of blue smoke if I hit the gas to pass someone, that is now gone. It also feels like it has more seat of the pants power. On the down side, my rear main seal has started leaking, and it is just getting worse. It typically will put a few drips on the ground a night. I'm thinking about running another application of Auto-RX this summer when I have more time to mess with it.
All in all though, I think it would have started leaking sooner or later, and I'm still glad I went ahead and did the Auto-RX application.