Chevys have a screw on the outside of the dist to service this. I imagine GMC is the same way. You remove the nut for the wire from the coil & the clip & wire. There is screw that goes over the shaft with 2 slots in it. You loosen that screw enough to remove & replace the spring & cond. wire. It takes a special tool, but you can improvise with a pair of small needle nose pliers or a tube ground down enough to leave 2 tips to fit in the slots to turn the screw.
George
