If your speedometer works, but your odometer (mileage counter) is broken then you can almost guarantee it because your old primary gear has failed inside. These were lubricated with grease when the gauges were built by VDO, and the grease eats through the gear over time, turning it into mush.
This new gear will fix that, even better it is manufactured from the best quality self lubricating plastic, so history dosent have to repeat itself (you dont use grease on re-assembly).
There are many variations out there and the only way to know if it is the right gear is to open your odometer up, and count the teeth!
Please do not ask me which gears fit which cars, while I have some idea for Porsche, you will still have to check yourself. If you are in a rush, you can buy a few different sizes and return what you dont need at your cost.
I also sell the following....just look in my eBay shop for the others....
==== IN STOCK : I keep the following gears in stock (1 day despatch time) =====
VDO "Twin" gears