E12 question reg. speed signal transfer

[shogun]

If I understand it correctly, the E12 does not have a speed sensor on the diff like all the later diffs.
There should be a mechanical system with a kind of bowden cable from the engine somewhere. It is a 518i, but the prob is, the car was made at BMW South Africa.
Someone on the German board was asking for the speed sensor, I told him on the diff on an E28. Now I have the feeling it is an E12 made in 1982. Probablty the E12 was longer produced in South Africa.
The E28 cam out in Europe in June 1981.

So the question: where is the drive for the speed indicator on the engine located?
He bought the car recently, but the speedmeter never worked.

And the funny thing is, that under VIN number on his registration papers it says
12821354.
But that would be an E30:

Daten für die Fahrgestell-Nr. '2821354'
Baureihe: E30
Fahrzeugtyp: 316
Typschlüssel: 1351
Motor: M10
Karosserie: 4-Türer
Katalogausführung: Europa
Lenkung: Links
Getriebe: Manuell
Produktion: 01/1988
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And what usually has to be repaired if the speedmeter does not work?