Cluster replacement?

Just got the car and PO told me it never since he bought it had a working fuel/temp gauge. Both are way up and over into the arc of the speedo. They do move about a tad but are definitely not working. The speedo did once read low and not return to the stop which went away with cutting the power and restarting. I have heard a lot about CLUSTER replacement and all the issues. I have been doing most of my own work for 30 years and this toss out fix it mentality is sort of new to me. Most times I find issues like this to be ground related or bad sending units, fuses and such.
So whats the skinny on the cluster thing and in my case the way to test it what to look for and in order of preference what to do to address it? I know how to remove the dash ect. I hate to just spring for a "new" cluster on a chance or have this one sent out under similar logic. Thanks.

Currently my RPM Gauge is sporadic epically on hot days it idles at 0. Which freaks me out. Next is my Temp gauge it is pointing when off toward the speedometer gauge and when is turned on and as the car is getting hotter its moves under where the temp gauge readings. Basically its as if the markings for the temp are laying on its side. Let me make a picture :).