How long was it since the last time you had the pipes off ? Here is my motto. If it isnt broke , dont fix it. If it`s not smoking, and building boost the way it`s supposed to I wouldnt worry to much. Keep an eye on it now that you know it is leaking. And see how much oil gets by in a couple days maybe even a week.
What`s strange to me is , how we get used to the way our cars run, and dont really notice the performance falling off, if its a little at a time. Then when you give it a tune up or repair a small problem and the car comes alive again. You go , crap ! it was running bad.