Thanks so much, this is exactly what I was looking for!! I actually managed to make the old keeper work. For some reason, the sliding glass door wasn't closing all the way into the keeper so I taped a couple spare nuts together and put them behind the keeper so as to make the keeper protrude approximately 3/8 out from the door (had to use longer screws obviously). It works fine now, apparently the keeper just wasn't sticking out far enough for some reason. If you know why this would happen, happy to receive any advice. I'd be open to buying the whole mechanism if you just think I'm using a broken keeper as the current solution is somewhat jenky. Thanks!
I think you door might be bowed. That would explain why the keeper needed to be brought out. Since you got the keeper working, leave it alone for now. Hopefully you gave it a few more years of life!
Is your door plum with the jamb? If you bring the door close to the jamb, do you see a straight line of light between the two, or is it wider at top or bottom?