1987 300TD Wagon - Speedometer question

[Chewable]

The Odometer is dead in my 1987 300TD wagon. I have another working one with almost the exact same mileage, but it is from a Gas W124.

I have put this into the diesel and it seems to work, but it is about 20% off. Reading about 48mph when I am actually going about 60mph (using my GPS to check it).

I have not found anything that says exactly what the differences are between the Gas and Diesel speedo setups if there is any. This speedo could be bad.

Are there known differences between Gas and Diesel Speedometers?
I would guess that the only differences would have to do with the cable somehow, because I cant find anything online that shows different parts for the two different types.

I am going to try and rebuild the odometer on the original speedometer and I also have a 1994 gauge cluster from a Diesel sedan that I will try to put in. I think that the later gauge clusters have better light distribution.