Change the oil and filter every 3,000 - 5,000 miles. Subaru dealer does the oil/filter changes, so I'm not sure what they use, but I refill engine with 5W-30 Castrol GTX when oil gets low. The first 60K was long commute driving (45 miles each way to work), from 60K-90K has been short commute to daily work (5-10 minutes each way). Lots of hills here in PA, but no aggressive driving.
BTW, I checked the antifreeze and see no oil residue. I'll check the air filter casing and PVC value.
Thanks all.