I have change oil in a 97 E320 twice. The first time I removed the filter cap and the cartridge stayed in the engine. I replaced the old cartridge with the new one and then screwed the cover on. I did not even think of snapping the cartridge into the cover because the cartridge did not come off with the cover. The second time same thing. I was concerned that I got the cartridge centered in the housing. I checked for leaks and everthing is fine.
So, on an E320 the cartridge should be snaped into the cover and then the cover and cartride "assembly" is screwed into the engine, correct? I assumed that my E320 engine was similar to oil change DIY article on this web site.