1999 Opel Corsa unknown cause

Electrical problem
1999 Opel Corsa Front Wheel Drive Manual 8275ml miles

I own a 1999 opeel corsa Eco. It's been very well maintained for the past ten years has had very little use, and has only a little over 8 thousand miles done. It had it's first service only today, but the problem is the speedometer stopped working, i'd thought it was just a loose wire, but he guy that did the service said it's not that, but he's not sure what it is, that it might be electric. And that i'd have to take to an opel dealer, can anyone tell me what it might be before I have to fork out more money.