I've used it.. It doesn't cause the seals to swell as far as I know, but it will clean out your engine really well. Adding it to the gas will lube up your fuel pump and injectors.. Will sometimes fix a malfunctioning injector. Run it through the intake, the white cloud of smoke is an amazing sight.. Can fix a sticky IACV. Cleans up your combustion chamber, carbon deposits, and lubes up the back side of the valve seals as well. They say to use it in your oil too, but I don't know about all of that. Most oil people you talk to do not advocate the use of oil additives. Except lucas, who sells them.. So they don't count.