We use a scope along with compression and leak down test.I would tend to think a piston problem.But you never know could be valves to.A leak down test would pin that down.A broken ring land most likey could be seen with the scope to
Yeah I feel like this has been an on going issue that has never been solved. When I brought my car in last year for an odd noise they told me I was down a quart of oil and that I had nothing to worry about. Once I went catless I started to notice the smoke. I've also had oil residue on my charge pipes that even when I clean them it comes back.