I noticed my front brake caliper on my 1978 240D is leaking brake fluid. What is the best way to repair this? I'd assume the easiest way is to just put a reman caliper on. There seems to be multiple versions of the calipers though. How do I figure out which one I need?

 

Can you explain why both need to be replaced at the same time? The one on the right side is new. The left side was not replaced by the previous owner and is now leaking.