I have an 89 300se with sort of the same problem. The last time I had this problem I had to have the injectors replaced which if I recall was not a real expensive job. My 300 uses or consumes about a quart to a quart and a half every 800-1000 miles. This seams to be a demon with the inline six's. My MB mechanic the last time did not say anything about the cold start valve, but he may have checked it and just not said anything. I would think that this could be a potential problem. I would have that checked, along with the injectors. I have run Dextron in the tank and even doubled up thinking that if they were extremely dirty, the double dose might do the trick. It improved, but is back. But, when I give a little gas before starting, mine seems to be a little rough starting but will start. I also have a 420sel and it doesn't have any of these problems. I personally think that MB skipped a beat when they came out with the inline 6. I have even had a valve job done and it did not fix the problem. It got worse and I took it back and the MB shop sent it back to the machine shop to have the heads redone and it came back the same as it was before having it done initially. I think the problem is in the heads on that motor as far as oil consumption. Let me know what you find out.