The coupe is a bit lighter in the rear than a sedan I believe (I have owned a CD and lots of 240s and 300s). the 280 is heavier than any of the diesel engines I think so that might contribute to the rear acting loose. And you did not mention tires. Tires are a huge part of good handling.

Yeah, the 123 will lean a lot but it will corner. I autocrossed one for a year and a half. The handling should be pretty neutral and it will corner hard once you get it leaned over if shocks suspension and tires are sound. I had h and r lowering springs on my 280e euro that I autocrossed and it did not help all that much because the sway bars are pretty soft. Good luck finding the springs and the after market sway bars are not available that I ever found for a 123.

Its not a sports car but it is a very competent family luxury sedan which will treat you right in an emergency situation.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.