I'm going to indulge here, for my fresh and intimate knowledge of the 'spring of doom'. I needed a tape, so I pawed through milk crates here at squatters camp and found what I took to be some rebuildable 50' tapes. As with a lot of projects around here, this may have had more to do with the resurrection than being cost effective.
With the spring out on the floor, splayed two direction or more; flipped first clockwise, then counter clockwise; trace back toward the innermost radius of the loop and find what would be the outside of the spring at that point. Follow that side all the way to the outermost loop, not minding the flipping and flopping at all. With the cup side of the blue housing facing you, press the outer side spring against the housing and onto the retainer pin so that it will wind into the cup in a clockwise direction, as you face it. Turn the cup like a little steering wheel, counter-clockwise, pressing and holding the spring in with thumbs and palms the whole way. The spring will follow easily. Place unit face down and walk away. I had a steel ruler I'd slip over the open face for handling otherwise.
The failing of two of these tapes was that the tightest radius of the spring would not bind on the tabbed bushing that drives the reel. You can give the spring new shape there with needle nose pliers.
I picked up new posts, screws, and belt hooks at the hardware store. I need a refill, but I see that Madsen's has repair ends. One tape is good enough to warrant that. we'll see.