Andersen window sash balances

A home owner from Portland, Maine says:
I have four very large windows with sash balance numbers:
P24 12SL 381
P23 12SR 481

The P24 came out easier than the P23, so maybe 1 had bee replaced?
Can you provide replacement units?
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Tom from SWISCO responded:

Hello! Thanks for contacting us. Based on your old stamps of "12SL" and "12SR," my respective recommendations would be our 24-13L and 24-13R Andersen brand sash balances.

Please let me know if you had any questions! We're always here to help.

How to replace an Andersen Window Balance
How to replace an Andersen Window Balance
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