Plastic tab for channel in sash vinyl window (Milgard)

Thanks for posting. This is called a Top Sash Guide. Its purpose is to keep the channel balance in a non-tilt window snuggly aligned with the window sash; hence why they are found in the top corners of the sash frame. When Top Sash Guides break, sometimes due to age or sun exposure, the channel balance will usually 'shoot' past the sash and lodge itself in the top of the window track, thus jamming the window. Replacing the Top Sash Guide and re-positioning the balance so that it is aligned with the sash fixes this. See the video below for guidance. 

Now, we've never found an exact match for this Milgard guide, but we have successfully used our 18-009 as a replacement. The catch is that you have to trim down the top edges of our part so that they're flush with the body. Review the dimensions below and let me know if they match what you need (ignoring the top edges, of course). Let me know if you have further questions.

Side view of 18-009

Detail of 18-009

Ah, I'm sorry to say that we don't. That damage is a little unfortunate since there's not a lot you can do about it. With the amount of constant pressure this part of the sash is under (from the balances), I'm not sure if I'd trust anything to hold. I would recommend contacting a local hardware store to see if they have a material they like to use in these cases. In a worst case scenario you may need to consider a new sash.