The lifters can be disassembled and cleaned. Usually they're full of varnish and soot and the little ball bearing "valves" get crusty. Don't waste your time with expensive oil or "treatment in a bottle" solutions, they won't fix the issue.

If the valve train is REALLY noisy, check for reduced oil flow. There is a passage in the head that can become clogged, or can become blocked by a migrating head gasket.

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Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]