I have repaired a good number of these. The wire stretches or breaks, making the shifter inoperative.
You need a 1/16" diameter steel cable, an actylene torch, and brazing rod.
Braze or weld a small nut to the top end of the wire.
Assemble the lever, and insert a bolt into the top of the lever to hold the wire in place on the T bar or ring. Duct tape the T bar to the lever to keep everything in the full down (normal) position.
Slide the spring and lockout dog onto the lower end of the lever, and wire it into place with the bottom end slightly inside the lever (ideally, it will be exactly even when completed)
Keep tension on the wire, with everything held in place.
Using a very small torch tip, braze the wire in place in the dog.
Trim the excess wire from the bottom of the dog.
If you can do this, you'll save the $160 a new lever would cost you.