Thanks all for responses, I will "change gear" and focus on cams and lifters. Just prior to taking that video I had the valve cover off to inspect the chain and I will post some photos below. Being new to this sort of maintenance, I'm curious as to what constitutes major cam wear. I did notice some scoring but I wasn't sure how much would cause issue. I have attached some photos and I will note that the lobes felt largely smooth apart from the dark portion on the lobe I detailed. I suppose cam wear on an engine with well over 400k miles is relatively normal and not indicative of any major issues, or is this a sign of failed cam oilers?

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1986 190E 2.3-16 202k
1987 300SDL 384k
1987 300SDL 295k (1 of 1 Dark Green over Maroon)
1988 300TE 129k (sold to buy cossie)
1989 560SEL 424k
1990 560SEL 288k (sold)
1992 300E 131k