Nice looking car and I'm sorry you are getting frustrated.
I'm a new 300D owner too so all I can offer to you are three websites that have been very helpful to me:
http://www.ps2cho.net/downloads/MB%20CD/W124/Main.html
http://mb.auto.pl/component/option,com_wrapper/Itemid,62/
This seems to only work in IE:
http://www.detali.ru/cat/oem_mb0.asp?TP=1
Using these websites and the help of the experienced owners of this forum you will likely be able to address all the issues with your 124.
Good Luck!