If you are not interested in the factory CD - try:
http://www.mercedesmanuals.com/
I am not saying they have anything of value - just pointing it out.
I have found value in:
Haynes #3253 - Mercedes-Benz 200,230,250,260.280.300.320
1985 to Aug 1993(C to K registration) Petrol and Diesel
Australian site provided below - I got mine in the U. S. years ago - try Amazon/etc
http://www.haynes.com.au/category35_1.htm