Here's what I did. I pulled back the spring using the jaws of a vise grip and clamped down on the plastic guide rod. Unable to remove the cap by rotating or pulling, I put the hacksaw to it. Obviously, there's no turning back at this point. Then, I released the vise grip and removed the spring. A word of caution, when releasing the vise grip, make sure the flange end of the guide rod is pointing at something that doesn't easily break.
Using the same method to pull back the spring and clamp down on the stainless steel rod, I removed the button head screw with an allen wrench. I exchanged the springs which happily have the same inside diameters.
Now comes the hardest part. I manually had to pull back this stiffer spring to clamp the vise grip on to the stainless steel guide rod. After that, it was downhill. I put some blue loctite into the screw hole and reinstalled the button head.
