VDO mechanical odometers are well known by Mercedes, Porsche, Volvo, etc. owners for being failure items over time. Without knowing what year your SL is, if it is a mechanical counter, then a speedometer repair shop, like www.paspeedo.com or www.nhspeedometer.com can fix it. There are other companies that can do it as well.

Since you mentioned SL500, I assume you have R129 body style, and a post '93. Your odometer is digital and therefore no mechanical parts in it. I am not sure you can fix the digital one and you may have to bite the bullet and get a new one if that bothers you. I am sort of surprised that your digital odometer fails at 67K miles.

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95 R129
04 Infiniti G35.5 BS
10 X204