Old windows need channels replaced

These are Milgard windows with a stamp of Jan 1993 on the inside of each window. This channel fell out which is how I am able to measure it. Length is 27 inches, width 1/2 inch. There is no window clip but only screws so I am not sure how to take out the other channels. Any help in this area would also be appreciated.

We had one window with 2 track fall out a few years back and had Milgard come out and replace them but they did not have the correct channels with them. Milgard replaced them with channels that do not support the window well and once opened completely it falls back down half way. However the channel pictured is an original.

I am unsure of the weight of window but it measures 46wx58h. There is one channel balance on each side of the window. Here are 2 additional photos of the window.

Thank you for your help, it is greatly appreciated.
Do these window balances come put together completely, or do I have to purchase and assemble all 14 balances piece by piece?