waldig-
Your posts are always a worthwhile read…keep ‘em coming!

Mine has had that same magnetic drain plug since its first oil change. MB’s ‘seal ring’ washer is N 007603 014106. Its copper material is more likely to inhibit leaks than a universal nylon piece. It’s not included with the Mann+Hummel fleece filter kit because the extraction method has become so prevalent. My parts guy invariably includes them gratis as penance for the thousands of dollars I’ve sent his way over the decades.