Already for a year or so my 4.7 is using oil, it was probably 3 Lts in 8000 Km. I changed the PCV twice and had an idea that it helped for a while, but then it came back again. Now its using around 1 Ltr in every 600 Km and i also see some smoke from the exhaust when giving gas. With 153.000 Km on it, would it be normal for the valve stem seals to cause a usage like this? Other then this or pistons oil scrapers, is there anything else to look at? Is there any way, without dismantling, to find the cause?