Identify part
Thanks for writing in! The white plastic piece in the window channel is the pivot shoe. This helps the window travel up and down and allows the window to pivot forward. To confirm the right replacement, I'll need to knot the dimensions for the width and the thickness of your shoe. It might be a good idea to find an undamaged show to confirm the measurements.
Also, since the shoe is broken, it would be a good idea to double check that the pivot bar doesn't need to be replaced as well. This is installed at the bottom of the window sash.
We do not have a direct replacement but our 15-046 Pivot Shoe will work fine in its place. It has the same dimensions you've confirmed from your shoe.
They would be the same for each side of the window.