James,
I've just been through this process.
Becker Autosound in New Jersey is who you want to use. They will refurb your whole radio for less than $200, clean it, replace bulbs, and fix your FM.
http://www.beckerautosound.com/I opted to replace my Europa mono in my 280SL with a Europa II stereo, which I bought from Desert Pagoda (on this site) for about $325. I also bought the kick panel 4" speaker housings from him, though I had to buy new speakers from Becker as well.
The DIN7 port on the back with the black plug should be on the mono as well. That was used for the old external 8 track/cassette units that were mounted below the dash. Ebay has a simple DIN7 to 3.5 mm cable/connector for about $50 US that will do the trick. When the 3.5mm jack is in, the radio is defeated, when out, radio plays fine. Watch the output on your ipod or similar mp3 device. some have regulators on the output, which causes playback through the radio to be very low, even with the radio volume turned up all the way, (which causes distortion as well).
Let me know if you need more information. You can do the whole stereo conversion for less than $800-$1000, but you can get away with $300-$400 or so if you just fix your mono Europa (probably want a new front speaker as well).