I think I posted a response to a thread you left on my original post. At any rate welcome to the forum. Not being much on here much longer than you, and owning a diesel MB probably the same amount of time I can only give observations from what I read. I have an '80 300TD which originally was delivered to me with 20W-50 and seemed to blow a lot less smoke than after the change to Rotella 15W-40. I now put Pennzoil multigrade 15W-40 to see if there's a difference. I get start-up oil burning then it subsides, but also have what I think is an oil leak through the vacuum pump hose to the intake manifold as well. You might want to check yours. Mine leaks at idle speed and can't tell how much during cruising speed. Most of that can be fixed with a new diaphragm kit from the part store. The other leaking you see on the back side of the engine is probably caused by a dry or brittle cracked valve cover seal which can also be bought from the parts shop. The blue smoke you see could be from a number of things as my thread points out, but start with the easiest first and elaborate from there if need be. Valve seals, to valve liners to piston rings and liners. Start with perhaps a different type of oil and go from there. Keep us posted on your venture.