Several of you may recall the grief I went through with the fuel starvation issues on my '82 300D. To recap, my car would start and run beautifully, but smoked profusely and wouldn't build any power above ~2300 rpm. I checked all of the fuel supply possibilities (ALDA, strainer, filters, algae, etc.) to the point of absurdity.
Finally, once I'd exhausted all of my ideas and the ideas of several very thoughtful list members, I broke down and left the car with my rather excellent independent MB shop. The owner of the shop deduced that the cause of the problem was the oil separator in the air cleaner assembly. The device had obviously been taken apart at some point as there was Permatex on the seams.
This is what was happening: The car would start and run. As it warmed up, the hot gasses from the valve cover were forced through the pcv hose and were diverted into the oil seperator assembly and forced down the oil return tube and into the crankcase. This had the effect of pressurizing the base of the engine! (Fortunately, it didn't rupture any seals.)
In retrospect, the two things that should have tipped me off to this were:
1. The "repaired" oil separator
2. The fact that I'd recently replaced the o-ring on the separator, thus making the pressurization possible.
Live and learn! Many thanks to the list members who helped out with this.