12 87 Andersen balance?

I need some replacement sash balances for our Anderson windows & I'm not sure what to get... so I saw your youtube tutorial and pulled back the plastic and recorded these numbers...

My sash balance numbers:
11600-17
and S8103/12 87

or it could be S81031 12 87 but the one following the 3 is a long line that does not look the the one after the S8

I'm guessing the 12 87 is date of mfg since that's about the age of the house.

Thanks,
Mike