Ciroen c5 2002 wp02 jvn?

I have a citroen c5 car and sometime the speedo work other times it does not. I have taken to the garage but they told me it needed a full cluster, I don't think it need a full cluster because is work but not showing the right speed cause i know that I am going faster than it is showing. Is their anything else I could get like a speedo & rev pointer needle, do you think this could fix the problem.

And who would fix this for me