Opened yesterday the engine for an valve adjustment, it looks like the camshaft got some wear, especially the first four "blocks" the other ones are smooth and show little wear. Is this something I should address or leave it for now?

And an other question, how do I see if there is any chain stretch on a '78 300CD?

Thanks

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1979 Black on Black, 300CD (sold), 1990 Black 300SE, Silver 1989 Volvo 780, 1988 300CE (vanished by the hands of a girlfriend), 1992 300CE (Rescue).

Here's a great thread about checking chain stretch.

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Rick Miley
2014 Tesla Model S
2018 Tesla Model 3
2017 Nissan LEAF
Former MB: 99 E300, 86 190E 2.3, 87 300E, 80 240D, 82 204D Euro
Chain Elongation References

There were some issues with the early MB cams wearing out. As I recall they were not sufficiently hardened in some cases. Will show wear on the tops of the cam lobes, will show darker against the bright color of the rest of the lobe.
I would not move to replace that cam until I had made some measurements on the lobe heights. Shouldn' t be too hard to at least roughly check the cam height on the lobes you suspect of wear against the rest.
Wouldn't be too hard to get a used cam to replace if needed, I think I have a usable cam around here somewhere.