84 300D turbo
I only recently received my MB shop manual on CD but you thread got me to finally take a look at the oil system. If I am understanding it correctly the part of the oil from the oil pump is going through 2 parts of the filter at the same time. The part of the oil that is going to the engine bearings only goes through the filter paper element part of the filter at the bottom.
The other part of the oil goes through the upper part of the filter with the cotton waste inside of it and down the center of the return flow pipe (the long stem with the 2 small O rings at the bottom) and through a check valve from there back to the oil pan.
Even after the oil filter thermostat opens and the oil goes through the oil cooler the oil is filtered the same. Part goes to the upper portion with the cotton waste in it and returns to the oil pan and part goes through the paper filter element at the bottom the filter and into the engine.
If the filter is operating normally and there is also cotton waste inside of the paper element part of the filter there should be no chance of anything from the upper filter getting into you bearings.
If something did get out of the upper portion of the filter with the cotton waste it would have to travel down the return flow pipe (where I feel I would most likely be caught in the check valve) would go down into the oil pan. If it did get past the check valve it would go into the oil pan. Something heavy like sand, rock, metal and ect would likely stay in the bottom of the pan. I don’t think that bug parts would damage the oil pump. Plant parts; maybe but they would probably float to the top of the oil. The cotton would be what I believe could possibly jam up the oil pump.
If something completely blocked the check valve in the return flow pipe the engine bearings would still get their full supply of oil but the oil pressure would probably go up and might open the relief valve in the oil filter housing (3.5 bar on my vehicle).
Personally I do not understand why anyone would filter part of the oil and dump it back into pan. I do like the idea that the oil coming back from the oil cooler is filtered as if you got anything inside you oil cooler hoses when you change them it will be filtered out.