When the 220D was the daily driver, I took the actual filter section and submerged it in a suitably sized container of diesel and sloshed it up and down. Changed the diesel and repeated once. Set it aside to drain for quite a while, then put new oil in the housing as per 'Addicted' and reassembled. Kinda messy, but seemd to work ok.

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1961 190Db retired
1968 220D/8 325,000
1983 300D 164,150