Kind of a hard question to answer. How would the user know if there were a problem or not. Here is my story. 170,000 miles on a 3800 V6, fuel pump never quit, fuel filter never plugged, car always started, I guess there were no problems.
I started using Fuel Power 60 and what did I find? The engine now runs smoother that it ever did, enen when new. The engine starts faster than before running FP60. And finally MPG went up by 1 or 2 percent, both city and hiway.
Did I have a problem before using FP60? Not that I knew of. Did FP60 make an improvement. You bet.