The xciting clusters are known for being glitchy. Corrosion on the contacts is common as stated above as is component failure. As Stig suggests, a dodgy earth is also common.
Mine is on its way out with a fading LCD and an intermittent dash light fault. I suspect there is a dry joint on the PCB somewhere in your case (I reckon this is what is causing my dodgy light connection).
Unless you’re a whiz with a multimeter or you know someone who may be able to track the issue down, I suspect your pcb is toast. There are firms online who allegedly can repair pcbs but it’s probably going to be just as cheap to keep a weather eye on eBay/gumtree/Craigslist etc to see if one comes up. They’re not cheap to replace with a new part at £227 a pop but I may end up going down this route myself simply as my scoot was originally a 500i and I’ve upspecced it to R trim. The instrument panel is still the old i-spec so it could do with replacing anyway.
Using second hand parts off eBay is always a gamble so unless you can find one properly cheap, you might be better off biting the bullet and buying a new one with warranty. Before you do though, make sure you are getting power to the plug block by using a multimeter. If you’re not getting a decent feed, your problem lies elsewhere.
HTH
Fav