Replacement Window Channel Balance Needed

A quick learner from Lake Forest Park, WA says:
Our circa 1977 home with the original aluminum frame windows (maker unknown) are starting to breakdown. I need to identify the correct channel balance (I hope I am using the proper term). Will you please help me identify this part and possible where I can order them?

The enire piece (pictured) including the nylon ends is about 28" long, 5/8" wide and has "26 4 JK CALDWELL" stamped on the outside.
User submitted photos of a window balance.
Profile picture of Tom
Tom from SWISCO responded:
Hey, thanks for posting. I've narrowed this down to two possible channel balance Series: either our Series 380 or our Series 385 balances.

Now, as you can see, there is only one difference between these two Series, and that is their bottom shoe. The Series 380 uses the 15-005 while the Series 385 uses the 15-004. I can't quite tell what you have based on your pictures, though. Please carefully compare their dimensions to your own hardware and see which is a better match.
15-004 and 15-005
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