I have a Corsa Milenium 2001 (Brazilian version of the Opel Corsa) and for a while now I've been having issues with my speed sensor (ECU light accuses problem in the speed sensor, code 24). The speed sensor is built inside the car cluster, driven by the transmission cable that also moves the odometer. The ECU light turns on usually when I'm going down a hill and not accelerating (engine braking) and turns off when I hit the gas for a while, and it turns on whether the speedometer is working or not.
Besides the speed sensor issue, the speedometer used to fail sometimes (going back to 0kph) and then suddenly get back to working. Now it's the opposite, it's mostly not working then at some rare occasions it pops up to the speed again (I believe it's probably a coincidence, but it's worth mentioning I think it switches more often from not working to working when the weather changes).
While the speedometer is not working, the odometer still runs fine, which makes me think it does not have anything to do with the transmission cable or the gear that passes the rotation from the transmission to the cable. Right now my best guesses are either the cluster itself (some problem on the speedometer) or bad wiring (the rest of the cluster is working fine though).
I need to decide between buying a new cluster or new wiring. Since they are both a bit expensive, I was wondering if the more experienced folks could tell me where are my best odds of fixing it (if I buy one and it doesn't work I'll have to buy the other anyways, but I was thinking if the symptoms could be pointing more likely to one of the causes).
Below just illustrative photos of the car model and the car cluster: