The cluster comes out easily. Take the plastic cover off, and you will see how it comes out. There are two, or three electrical connectors and the whole assembly comes out.
You are correct that it is a solder connection. Once you get the cluster out, you will see the printed circuit board (PCB) will have revits that connect top and bottom PCB traces. Solder reflow ALL of these revits, clean the connections to the tach driver board (a daughter card tha plugs into the back of the tach) with a pipe cleaner soaked in contact cleaner, and you should be good to go.
If you can't solder, you can take the cluster to a speedo reapir shop, and they will solder reflow, calibrate, and test the cluster for 100 to 200 dollars.
Good Luck,
Bill
