I had a clip, not a nut. Was concerned at first that I wouldn't be able to remove without damaging the clip. I used a pair of pliers to ease it off. Can't remember what I used to remove the old filter, but it came out without problem. Reused the old clip to compress the spring that holds down the filter. Seems to work just fine.

PS I used my MityVac to remove all of the old oil, and really scrubbed the inside of the oil chamber with a rag to remove all of the accumulated crud.

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1989 300E
103,500 miles

1982 300SD
Sold but not forgotten