Mines the same way. I haven't changed it yet. I just went through hell changing the clutch master on this car and have just wanted to drive it and not work on it. I think you might have better access by taking off the secondary filter. It doesn't seem right and I assumed it was screwed up by the previous owner but after hearing about your situation I'm not so sure. I have the paper FSM for the 201 and maybe that will clarify. I'll let you know.

Kevin
1979 240D manual
1984 190D manual