Top Sash Guide ID

Hi,

I'm interested in identifying the part shown in the attached pictures. Its "job" seems to be to help guide a metal part that fits through it and that slides through it, allowing the window to be locked or unlocked. The metal part that slides is shown in the photo labelled "installed.jpg". The window is about 20 years old and is a white vinyl, awning-type, measuring 5' 3/8" x 1' 9 5/16". It lacks any identifying markings, but the window was manufactured by an outfit named Starline,

Thanks for your attention