Does the car have the original mechanical odometer or does it have a digital dash?
The original dashes had real speedo/odo electromechanical units. The digital units have separate readouts that are just computer outputs.
No matter what unit it is you should take it out and send it to Beckman Technologies in Durham NC 1-919-381-2700.
Bosch Master, ASE Master, L1
33 years MB technician