The thing that isn't shown clearly in the diagrams is that there are teeth or ears on the right end of the spring (#11) that engage with teeth or ears on the inside of the end cap (#6). The ones on my end cap were bent over and causing the spring to slip and lose tension. You could wind the spring the right number of turns, and install it in the end cap, and tighten everything down and it would seem just fine. A couple of cycles of slide extension and retraction later, the spring end would have jumped the ears on the end cap and have lost tension to the point that it wouldn't retract the topper. The crew at Talin RV in Brooksville (run by @throgmartin ) found this issue for me (great folks!) and put a new end cap on mine -- problem solved!
Does yours have the center cover support (#8 in Detail A)? If so, that is another source of various issues (sagging, friction, bowing the roller tubes). It will need to be shaped correctly and secured with a stainless cotter pin (not shown) to support correct functioning when the roller tube is longer than 12' because it then has two sections that are sleeved and riveted. Carefree has a newer and better digram if you call them.