What Horehockey was talking about was not getting into the instrument cluster but trying to tighten up the connections of the black plug that attach to the back of the instrument cluster.
First remove the speedo and the tach cables from the back of the instrument cluster. There will only be in they way if left attached.
You should disco the bolts on the bottom of the instruments that hold it to the bracket.
You'll see where the wiring harness plugs into the cluster. Pull up and twist just enough so you can use a small Phillips screwdriver on the tiny screw that holds the wiring harness plug.
It is the small connections in the wiring harness plug that need tightening. The cluster has a series of pins in it's back. The cluster should be completely free of the wiring and the entire motorcycle by this time, set it aside. These pins that you see in the instrument cluster mate with small metal sockets in the plug. The female sockets in the plug are a typical sort of construction for this, of this vintage. The sockets are split on one side. They are a soft metal. Using a small sharp pointy object they can be tightened by inseringt said object into the rubber along the side of the socket. Compress the socket a small amount.
This is a delicate operation but doable by almost any sober person.(did he really say that?) (Yes, I did)
There are things inside the instruments we sometimes try to repair. There are a few things you may someday want to investigate. But if you have no reason to open the cluster up at this time then leave it alone. If you do open it up or anytime you open it up the first thing to know is the small screws used for holding things together do not get a lot of torque. Over torquing the screws will cause water leakage and more problems down the road. The cover screws especially go into small brass inserts in the plastic cover and if over tightened they will crack the plastic.
Put everything back together, small screw in the plug to hold it. And the speedo and tach cables. I put these on finger tight and then add a small amount of torque with a Chanell lock pliers. Only about 1/8 of a turn. Careful not to scratch the knurled nut.