avengence

Ok so my car has been having problems for about a year now where the voltage gauge would go up and down. Some days it would be over the max some days it wouldnt even move. Today the speedometer didnt work. I have already changed the alt but I havent changed the battery yet. Never had a problem starting but the battery was pretty badly corroded at one point. I cleaned it and put the grease and felt circles on it and the corrosion stayed gone.

So do I need to replace the cluster to fix this stuff? Its intermittent and is totally random. If its not the cluster could it be wiring to the cluster? Thanks!