I was looking at frame 1:08 on first video, it looks like your head gasket isn't seated tightly...oil (is your oil running low)?

Are any of your fluids running low? I recently bought a older mercedes which smoked terribly (no one could figure out what is was)...turns out it was brake fluid leaking onto exhaust resonator. The clue though, was the fluid kept running low (and everytime was at stop light (ie, compressing brake), would start to smoke.

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Current:
1971 Mercedes Benz 250 (Euro Spec)
1972 Mercedes Benz 250 (US Spec)
Past:
1972 Mercedes Benz 280