Seatbelts aren't complicated: it's a spring, a drum, a belt, and a couple of bolts. When you buy new seatbelts, it all comes in one piece; the hard part is figuring out how to attach it to the car. The car in question is Sam's Porsche 924, and the seatbelt in question is the driver's seatbelt in Sam's Porsche 924.
There's not much more to say about replacing seatbelts. Good old West German engineering meant that it was a 20-minute job. Now the seatbelt returns promptly and with a satisfying thunk. In the event of a collision we're now minimally safer than we would otherwise have been.