Part needed
That part is called a pivot shoe. We may sell a match for yours, but I can't quite make it out from this photo. It's a little too obscured.
The best place to start would be to submit a photo of the pivot shoe removed from the window and clearly shown without obstruction. Knowing its width and thickness would also be a huge help. I can then check our inventory for a potential match.
You would first have to remove the balance, taking care to first retract the shoe and cord all the way before you do so. Once the balance is out you should be free to slide the shoe up to the cutout at the top of the track and pop it out.
If there is no cutout, then you will unfortunately have to make one. The video below will show you exactly how this is done. If you're not comfortable making these kind of alterations to your window yourself, you may want to seek the aid of a local professional to do it for you.
Thank you! These photos are a huge help.
So, my best suggestion right now is the 15-129. It looks very different at first glance, but I think that they'll end up being nearly identical in all details except for height, which doesn't matter so much. Width and thickness are far more important, so your next step should be to check those measurements to verify that they line up. I'll share a diagram below that you can use as a reference. Like I mentioned before, height isn't important so you can ignore that.
Otherwise, they appear to function the same way. The 15-129 is compatible with all the same hardware you have in your window already, like the balance and pivot bar, and serves the same function. As long as the width and thickness are the same then I think you'll be good to go.
