I owned not one, but TWO Manganese Brown W123s. My W123 240D, but also my Turbo OM617 300D. They were gorgeous, well my 300D was nicer because it didn't have any rust after I had paint work done. The 240D had nice paint, but the rust holes ruined it and made it look like a survivor.

Though in seriousness, stick with what you have. Manganese is a timeless paint job when it really shines and it does look very classic. It stands out next to green, blue, grey. What other car than a W123 can rock Brown and look good?