i'm burning a 1/4 to 1/2 qt a week, lots of soot at the tail pipe but no smoke and no leaks, the oil is really black a couple days after a change. i dropped the downpipe and the turbo has no play and clear of soot,it boost fine.there's no oil in intake tubes and i did the rubber glove test on the oil filler tube and i'm getting some vacuum. the one way check valve works. compression test was 170+ on all cylinders.i did notice the #3 spark plug was really gunked up,black and white build up but it wasn't wet, the rest were ok. plugs are 4 months old, cassette is new, i use 10w 30 0r 40 it's an 07" with 115k. what else should i check to solve this problem. thanks in advance