Alright everybody, I've got a solution to a notorious Volvo problem. I was messing around, attempting to fix various annoyances in my car, when I decided to pull off the seat cover and see what was wrong with the lumbar support. In the process of fiddling, I figured out how to fix it for next to nothing in about 30 minutes!

Start by removing the lumbar adjustment knob. Just rotate it counterclockwise until it comes out, then pull the plastic shaft holder out with it. You can pull off the seat cover by first removing the 5 circular metal clips that hold it together at the bottom using two pairs of pliers. After that, you just slide the cover to the top of the seat like taking off a shirt. Once the back of the seat is exposed, the lumbar support system is too. You'll probably quickly notice what broke: one of the two wires holding the plastic lumbar support. Whichever wire it was, remove it from the seat back, noting the holes it snakes through on the side of the seatback frame. Then take a thin wire coathanger, bend one end into the proper loop shape, slide the other end through the holes in the side of the seat frame, size up how much more hanger wire you'll need, cut off the unnecessary amount, form the other end into a loop, slide the wires through the clips on the lumbar support, attach the loops to the tension springs, and you're done! Congratulations, you just saved $20 plus shipping over a repair kit. As an added plus, the coathanger wire is a lot stronger than the original parts!