Replacement Channel Balance - Confirm Model

A home owner from Valencia, CA says:
I'm replacing the channel balances for a window. I am pretty sure that I need model S385-27 but I'm not sure of the stamp option. Attached is a photo of the broken one with the model markings on it. Can you please help me confirm what the right replacement would be?

I also need the channel guide for at least one side. Do you recommend replacing both sides? Part number (I'm fairly certain) 18-188.
User submitted photos of a window balance & top sash guide.
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Tom from SWISCO responded:
A stamp of 26 4 usually corresponds to our 2640 option, but you should weigh your window sash just to be sure this is correct. The S385-27 has a chart that relates each option to a sash weight. Check it out for reference.

I cannot tell what top sash guide you have based on just this picture, but I can say it looks a lot like the 18-188. You're going to have to compare dimensions to be sure.
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