Channel balance with no number

A handy person from Northern California says:
March 9, 2013
I have 4 identical windows that all slowly slide down when opened. They have been installed for about 15 years. Would applying oil to the pulley bearings help or make matters worse?

I have what appear to be 22 in long S351 style channel balances, but with no 4 digit number on them. One of balances has an ink stamp of

21 5 CU CMC 4

The windows weigh 33 lbs. What 4 digit number version should be ordered if replacement is the right answer.

Doug
User submitted photos of a window balance.
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Tom from SWISCO responded:
March 11, 2013
Good morning, Doug. Thanks for getting in touch with us. After 15 years, I don't know if anything will really do much good. It's probably time to replace the balance altogether.

I agree with you--I think our Series 351 looks like a pretty good match. With a stamp like 21 5, I'd usually recommend our 2150 option. However, two balances with the 2150 option can only support a window sash weight of 23 through 27 pounds. Can you confirm that the length of the metal channel is 22", and that the window sash weight is 33 pounds? If so, then your balance may need to be custom made.
A handy person from Northern California says:
March 12, 2013
Yes, the metal channel is 22 in long and it weighs 33 pounds.

Doug
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Tom from SWISCO responded:
March 13, 2013
Thanks, Doug. That should be all the information we need. Take a look at this Custom Channel Balance Order Form that I've started for you and fill out the rest of the information. One of our representatives will get in touch with you shortly thereafter.
22" Series 351 Channel Balance
22" Series 351 Channel Balance
S351-22
$9.91
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