W123 is a chassis name that covers the range of models (somebody correct me..) 1977? to 1985 inwhich many parts are interchangeable, from doors, to seats, to windows. It includes the 240D normally aspirated Diesel and 300D turbo Diesel models. This is the most successful and widespread model Mercedes made.

Mercedes stopped building cars on the W123 chassis in 1985. After that they introduced the W124 chassis which goes up to the mid 1990's and which I think? includes 300E Gas and 300D Diesel models...

Can anyone add to this?