Any special tools required?
Hair dryer. Use it to heat up the seam to make the old seal come off easier. Start peeling the old seal off and then just work your way around the neck opening. Once it's off, work on the old cement/sealent. You don't need to take it all off. Just get enough off to give yourself a smooth surface and edge to work with.
Large bowl or jar (like a Costco industrial size mayonnaise jar). Put it upside down in your suit at the neck to give yourself a form to work around. Your suit should be inside out if the seal is glued on the inside. Turn the neck seal inside out and place it on the bowl/jar. Set it in place. Peel back the bottom edge of the seal so the fold meets the dry suit neck.
Flux brush (available at your local hardware store in the plumbing section). Apply 3 coats of sealant to the dry suit and the neck seal waiting 10 minutes in between applications. After the 3rd coat, carefully unfold the neck seal onto the dry suit. Start on one end and work your way around being careful to not create any creases or folds. The cement is very tacky and once both sides touch you will have a difficult time fixing any imperfections. Once the entire seal is in contact with the dry suit, apply pressure around the neck. You can use a roller, but I always just use my hands. Inspect your work to make sure it looks like you have created a seal. Let cement dry for 2-3 hours.
When you return. Measure and cut a length of seam tape to apply along the inside seam. Apply 3 coats of sealant to the seam tape and the seam (just wide enough for the seam tape), 10 minutes apart. After the 3rd coat, careful work the seam tape around the seam applying pressure as you go. Make sure you have some overlap at the end. You'll need to apply a little more cement on the first end you set in place so the overlapped end will stick. Apply pressure around the seam tape. Let cement dry for 2-3 hours.
You are pretty much done at this point. I go through the added measure of putting a bed of aquaseal along both edges of the seam tape and letting that dry another 2-3 hours. This takes about 5 minutes to do.
It's real easy to do. I started doing this a few years ago and now I always have spare neck and wrist seals at home and can replace seals as needed. I just reorder seals as needed to keep my stock up.
If you want to attempt this, but want to talk about it, call me at 850-272-7484.