For the oil, just use the Subaru motor flush or Gunk motor flush, just don't drive the car when it's in there.
Warm up the engine for 5 minutes and change the oil.
I have dumped Seafoam in the gas tank, once too.
175,000+ miles, 5/20/12 new ej257 short block, 8/20/11 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. Also CHECK YOUR OIL, these cars use it.