OK... The bimetal beam should be arrow straight. If it has a bow at room temperature it has been overheated. You can straighten it by hand but it may not respond properly to temperature change.
They aren't all the same. In the most common type, Approx' 13.5 inches of wire required. It's 1.5 ohms per inch at 68 degrees so gauge total is somewhere between 20 and 21 ohms at 68 degrees. Approx' 17 inches of 1.25 ohm per inch wire will fit in there. 20.5 inches of 1 ohm per inch wire will not.
Solder doesn't stick to nichrome so the wire is/was welded to the stud. The wire work hardens at the weld and would break so a dollop of cement like material is added to keep the wires movement above the weld. Find the wire. Figure out how to attach it to the studs. Just ship it to a gauge service. Good luck
