Need to rethink exhaust noise.
 

1978 116.033 M117 4.5l engine.

I can't find any exhaust leaks to atmosphere.

I did take apeek under my oil fill cap and saw grooves worn in whatever is immediately inside:eek:
can a bad/broken/worn camshaft make a RPM variable tapping clinking noise? kinda sounds like a little miner picking away at a metal tube with a pick-axe.

No oil leakage, no oil burning, no smoke whatsoever. EASY starts, good oil pressure, no missing, no rough idle (when it does idle at it's normal RPM)
Noise seems to get duller the hotter the engine is, like sitting at drive-thru, when it gets up to about 100 the tapping noise is a bit duller, but still there.