A home owner from Kerrville, TX says:
June 17, 2014
Do you have anything like this? My aluminum windows use these plastic (delrin?) parts to slide along the track. They are attached with the same screws that hold the frame together.
Dave from SWISCO responded:
June 18, 2014
I can't seem to locate a match for your window guide. Take a look at 87-050, though. Could you retro fit this? Basically I'm thinking that all you need is a small nylon block with hole drilled in it.