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.
199,000 May 12 new ej257 short block, Aug 11 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. CHECK your oil, these cars use it.
Engine Build - Click Here