This is the rivet that holds the aluminum disk onto the button under the boot. There are two ways to remove it, shown here as options 1A + 2A -or- 1B + 2B. Select the method that works best for your tools, abilities, and patience. There is a third method which leaves less damage, but requires custom tooling. Special note: if you look through the spring and see a hex/allen head, you have an older style that is easier to disassemble. Remove the spring (step 1B) and then simply unscrew it!
Place your Z41 on a clean, non marring surface. This can be wood, plastic or even an open phone book.
Then position a flat headed punch in the exact center of the old boot. 3/32" (~2mm) is best. No bigger!
Strike the punch with a small hammer until the metal assembly drops out, 2-3 times should do it.
This leaves everything in perfect condition, except the boot. It will be scared and possibly torn/punctured.
Place a small flat headed screwdriver into the side of the spring. Then rotate your tailcap so as to force the driver into the lower coils. As you go, stop rotation long enough to try levering the driver. Continue to turn and lever, until the spring pops out.
While bracing the tailcap, use a strong pair of narrow pliers to secure and then pull on the aluminum disk inside. This may require considerable force, potentially damaging both the aluminum disk and gasket. Baking (or boil in a cooking/freezer grade bag) your tailcap for 10-20 minutes (2-300 degrees) may soften the plastic that is holding the rivet. Let it cool before handling!
Once the metal is out of the way, what remains is a plastic nut/disk. This is usually held in place with adhesive. Baking (or boil in a cooking/freezer grade bag) your tailcap for 10-20 minutes (2-300 degrees) may weaken the adhesive enough to make it easier to break loose.
Insert needle type pliers into the slot and hold them pressed both down and outward, toward the ends/outside of the slots. Then turn (unscrew) the disk. This may require considerable force, depending on how secure it is. About a third of all tailcaps cannot be rotated without baking, even with special tools. Let it cool before handling!
Consider cleaning your tailcap (especially inside) before proceeding. If using soap/water, let it dry.
Place the new boot (taller and with a smaller flange) inside the empty tailcap.
Using your finger, press it up through the hole and check for even/square installation.
Step 5 (not shown)
With the switch already inside the brass ring, hold/pinch the spring with your thumb and first finger. Gently square the assembly inside the larger tailcap opening, locating the threads. Spin the tailcap with your other hand, starting the threads. Continue spinning/tightening the tailcap until your fingers are well inside the tailcap.
Insert long/narrow pliers into the torque slots of the brass disk. Hold the pliers in such a way as to apply outward pressure on the handles, then begin to tighten the assembly into place. As you finish, check the boot again for proper alignment (centered etc.). Then tighten down the disk the rest of the way. When ready, release pressure on the pliers before pulling them out.