I had an oil consumption issue with my 91 350sd, om603. Couldn't find it for a while. The underneath side of my hood; hood pad; was getting wet around the oil filter canister. But it wasn't my oil filter housing. Finally figured out my turbo was leaking and making a mess in my intake manifold and oil was leaking out around the boost fitting/line on intake manifold and making a mess. I changed out my turbo with a used one I had with @ 100k on it and went from a liter of oil every 800 miles to @ 1 liter every 1500 miles, with @ 400k on engine. So a seal somewhere in the turbo went bad.