[2012 Outback/Legacy 2.5 CVT transmission]

I would think there is some difference considering price difference, subaru dealer can tell you what will work junk yards can too. 

[Change the Exhaust system]

WHEN YOU CHANGE THE SYSTEM IF ITS NOT THE SAME FREE FLOW OR BACK PRESSURE  HOW EVER YOU WANT TO LOOK AT IT YOU WILL HAVE MAKE A CHANGE IN THE FUEL DELIVERY. Engines that i have worked on is always more free flowing for more power which equates to having to make fuel system richer, more gas, Something you may have to play around with to get it right on.

[Checking the oil in an EJ]

Always check oil after car sits overnight that will give the most accurate reading and easier to read. 

[drastically reduce oil burning]

I have owned 3 sybarus in the last 15 years all with 2.5 boxer engine. They all started to burn oil at about 30 thousand miles I tried many types of oil with no change in oil consumption untill I used AMS OIL. What a difference only burns about  THIRD of what it did before which was a quart in 2 or 3 thousand miles. The oil is more money but you use less aver all oil. YOU cannot go wrong with AMS oil.