Anderson Sash Balance tension cord

One of the left tension cords broke and i have to repair it. I have removed the left side sash balance tension cord unit(I left the right one one for now so that there is some tension on the window sashes until i can replace both tension cord units). The markings on the unit are:

E43 9P27 377

These windows are circa 1977/78 I think. Could you let me know which parts would be appropriate replacements? Thank you in advance for your help!

Vince Walters