fxdave: If the awning retracts correctly, it is probably not the springs. There is a ratchet assembly inside the end cap that locks the awning retracted, and if that is slipping it will probably need to be replaced.
My ratchet broke and was replaced in 2006, The spring, locking ratchet and end cap came as a unit. The new rachet was more substantial and held the awning more firmly. (It had bigger/deeper teeth. Price to replace then by Grace & Son RV Repair here was $137, parts and labor.
I also installed an awning lock on the other end of the awning. This unit here.
Which RV Awning Travel Lock Do I Need?
hope this helps..