I would stop driving it as soon as possible. A cam oiler fitting or several of them has probably come loose and the cam is not getting properly lubed thus the valvetrain noise. Hopefully you haven't scored the cam yet. Pull the valve covers and see what you find. Might be time to service the timing chain, guides and tensioner anyhow.

Cam oiler tube fittings are definitely a wear item on these v8's. They will also cause an otherwise seemingly healthy engine to use oil, once the oil tubes pop off oil is pumped in massive amounts into the valve area but not onto the cam as it should, rising to high enough levels to overwhelm the valve seals which are probably weak anyways.

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Chas

Had a 380SL, 450SL, 380SEL, 420SEL, 500SEL

Got a Euro 500SEC right now.