Coupling Problem between Leica M3 and Summicron 50mm 1969-1979 version

[nobbylon]

Same lens at infinity,

your lens has normal markings.

 

[Landshark]

Occam's razor?
The answer with the fewest assumptions is usually correct.
So.
Assume your repairman isn't that familiar or at all familiar with Leica.
Assume the camera is at fault with regards to the error in the rangefinder. It's extremely common. Far more so than the lens being incorrect.