[telyt]

The Leica 50 1.4 and the Contax 50 1.4 come off the same Zeiss assembly line.

This is not correct. They are different designs and made on different assembly lines on different continents.

As for the original question, the R4 is not considered one of the more reliable Leica reflex bodies. I would suggest the R5 or newer including the R-E instead.