Channel Balance- Which one do I need?

Since your old stamp reads "23 2," then you want to go with the 2320 option.

You can't determine the Series from the stamp option. They're not part numbers or anything, they just indicate the strength of the spring. There are actually dozens of balance Series that use a 2320 stamp and all of them are different. 

To determine the Series, you need to compare the style and size of the top and bottom nylon fittings to those balances we show on this page. There's no number, code, or sticker that will tell you what to choose. The only way to know what to do go with is by comparing the physical attributes of those fittings.