MPG, Soot, and leaks

[ascalise]

I just got back from a 600mi trip. My SD only got 21.5 mpg averaging about 75. When I got there, I noticed lots of black soot all over the back of my car. Is it running too rich? My mechanic tells me that I have excessive blow-by also. Another MB mechanic says that my leaky exhaust could be a problem. The car is also leaking oil horribly. Before I left for the trip i put in about a quart. When I got there (300mi) I checked the oil and again put in a quart. I havent checked it since I got back but it seems like its either leaking way too much or burning a little and leaking alot. I just had the valves adjusted and the valve cover gasket replaced. It seems that it leaks more oil than ever now. I already have oil seeping up the front of the valve cover gasket. I had to tighten the bolts on the valve cover 3 times to get the leaks to stop from the studs/bolts. I also bought the turbo oil return gasket, seals, and grommet. What other areas should i check. I have about 10 spots underneath the car that oil is coming from. I've degreased the engine but still can't tell where any of it is coming from since there are so many leaks. I know for a fact that the lower oil cooler hose is leaking at the cooler and possibly the other end. I also know that the oil return line is leaking badly. All in all i'm spending too much money on oil! :-)