The CD player in my 1990 300D is a six-disc Blauplunkt. It still plays fine, but even better is just ripping a dozen or so of the best CD's into MP3's and playing them on an MP3 player. This you can play with an adapter in the form of a cassette that plugs into the cassette slot.
You can get over 10 songs on one disk. the sound quality seems just as good, you aren't i danger of damaging the orginal disks, and there is a readout on the MP3 player that tells you what is playing. No more having to memorize Track 4 on disc 3.
The best MP3 seems to be the Rio SP250, which Amazon will sell you for about $134.00 delivered. Or you could bid on E bay, where someone bid one up to $165.00. This model also has an FM radio, a lighted display panel and rechargeable batteries. I imagine that there are other good MP3's as well.
A note: when it refuses to play, the batteries need recharging. One charge is good for about 10 hours, it appears
Semibodacious Transmogrifications a Specialty
1990 300D 2.5 Turbo sedan 171K (Rudolf)
1985 300D Turbo TD Wagon 219K (Remuda)
"Time flies like and arrow, yet fruit flies like a banana"