Hey guys. I actually went in and did the fix mentioned above to tighten the spring. It did not work for me, and led to even more problems. Beware.
There's a lot of tension in that spring, and as I was carefully winding the spool I accidentally slipped and within a nano-second it lost tension and unwound entirely. Had it been a simple matter of rewinding the spool it would have been OK. Instead, it was a catastrophe.
The spring pops out of the slot on the small plastic piece in the center with which you rewind the spool. It's barely stuck in there for some reason. All of the sudden you realize that there is no way to access the dislodged spring to reinsert it into the slot of the center piece so you can rewind the spool. I'll continue to tell the tale only to help anyone who goes to the dark side and needs to know the way back without spending $162 for a new assembly.
To get the spring back into the slot, you have to open the "DO NOT OPEN THIS" cover on the spring cover. Pop the plastic spring case off of the seatbelt assembly to access the cover underneath. Wear safety glasses and keep a thumb on the spring to ensure it doesn't pop out of the case. Super-glue the spring and reinsert it into the slot on the center piece so this can never happen again. Use a screwdriver to push the center piece back to the center as you use your other hand to maneuver the cover back on.
Get some twisty-ties to tie it back to the metal through the holes where it had previously attached because now that this "DO NOT REMOVE" part is off, it doesn't want to reattach easily, the pegs break or become weak, and you don't want it popping off or else more fun happens and the spring could shoot out and cause you 30 minutes of hand-cramping and suffering to get it back in. I speak from fresh experience.
Once it's reattached, wind the spool toward you, then slip a piece of kite string through the small hole on the belt spool and tie it off so it can't slip while you reattach the belt end-loop through the center of the spool. The easiest way to do this is to jam the belt through the small slit at an angle and grab it with needle-nose pliers to yank it through the other side. Replace the plastic piece which keeps it from going back through and untie the string. Let the mechanism retract and you're done.