A friend of mine has a 2011Toyota Prius 3 : 2ZR-FXE : 1.8L 4 cyl. with 95k on it. He’s having to add about 1 quart every 900-1000 miles, it holds 4.4Qts of Ow-20. Second owner at 50k. He says there are no leaks he can see on the driveway or elsewhere. From what he’s told me it sounds like the engine has always been driven very easy, all low rev’s. I’m no mechanic but it sounds like carbon / gunk formed on the piston rings or ring lands. The way they get driven it seems like destiny. Any options for him ? I’ve heard the Kroil application mentioned in the past. Thanks