[cptmclark]

Much more fun than simply calling the manufacturer.

Remove the vertical adjustment screw (carefully as there is a spring involved) holding the sight down with your thumb. Notice that the vertical pin is now probably free to move up and down. It shouldn't be, but it is. When the pin is down, and the sight is up (beyond its adjustment range cause the screw is removed) you can see the spring in its hole, fore and aft, which should be protruding into the space occupied by the pin and holding it forward, except it ain't. On mine at least, the spring was too short, obviously from being compressed these 35 years, and no longer supplying pressure against the detent pin. Not having a new spring for a proper fix, I simply stretched the old one, reinstalled (no small task in that tiny hole). By compressing the spring out of the way of the pin (which is below the hole when the sight is raised above its adjustment range) you can press the sight back down over the pin, release the spring against the pin and while holding down firmly on the sight, replace the adjustment screw, and voila!... she works again. I'll order the proper spring for a real fix, but don't know if my nerves will allow me to fuss with those tiny parts again.