Small clear plastic part

Thanks for your post! The part you are missing in the window appears to be the mounting bracket for a coil balance assembly. We do not have an exact replacement match for the one you have but there is a good chance we can provide a suitable alternative.

May I see a photo of the coil assembly installed in the window track? I'll need to see it to ensure our replacement would be compatible.

Please let me know if you have any questions.