I don't know if the S-Class's odometer/speedometer is the same as the E-Class, but mine went out too (my speedometer is fine). Here's a picture of the gear that failed.
http://www.peachparts.com/shopforum/showthread.php?t=270146.
I contacted a company that sells the gears and this is what they said about the missing gear in the picture:
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The small gear is part # 10-022, 12 tooth gear cost is $28.00 which includes US Mail Priority to anywhere in the US. However the other two gears in this picture are made of the same poor plastic and also break. The other two gears are a 12/48 gear which is $32.00 and 16/48 gear which is $32.00. I would recommend replacing all of the defective gears but if you would just like to purchase the small 12 tooth gear you can order it over the phone using a credit card or on my website using PAYPAL. If you have any more questions please let me know.
Best Regards,
SOUTHERN ELECTRONICS Inc.
Authorized Car Radio and Speedometer Repair.
730-A Research Road
Richmond, VA 23236, USA
Tel: 1-800-446-2880 USA Toll Free,
Tel: 1-804-423-1100 USA Local and International
Fax: 1-804-423-1059
Business Hours 8:00 a.m. - 5:30 p.m. Weekdays (Eastern Time, -5 Hr. GMT)
Best time to call 10-4.
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Http://www.InstrumentClusters.com Speedometer & Cluster Repair
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