I'm no subaru expert, just an electrician thats dismantled a couple legacies to make one. I used seafoam once in the gas, didn't notice any butt-dyno gains after or if it had done anything. It says on the back not to use in engine oil for turbo applications. I used it in project porschit, sucked it in thru a vacuum line and revved it for 20 minutes, so much white smoke came out, neighbors were kinda trippin at first. I think black chunks were coming out, but it could of been the rusted out muffler blowing apart. did almost the whole can, drove it a bit, pulled the intake off and it was still coated in black crud, but it was wet and when i wiped it, it came clean. So the solvent works but the crud was still there, maybe after a gallon of it it would clean itself. 02RS recommended marvel mystery oil to use in the oil and clean the internals, sometimes I get the noisey lifter annoyance, mostly under warm-up. Going to try it soon.