This is copied from an earlier post I made regarding gasket replacement.
Good quality, well done, do it yourself gasket replacement is actually pretty easy. I've only replaced my own neck and wrist gaskets over 10+ years of boating with this technique: (peel back the neoprene over cuff and keep it out of the way)
Remove all traces of the old gasket and glue. If it's new, there may be a stitch line, don't be afraid to use a sharp knife and deft hand to remove the stitches and then peel of the old gasket shards. You can do it!
Get the good raw fabric cuff out and accessible. Take a common rubber ballon and begin to inflate it by mouth, inside the cuff. When the balloon is getting close to the size of the fabric cuff, keep inflating and smooth out the newly tensioned fabric. Don't over inflate, but get a bit of a pooch out in the balloon above the fabric. Tie off the balloon.
Take a breath. Position the balloon so that the fabric cuff stradles the balloon right at its midpoint. Now, take the dry replacement gasket and put it onto your new rubber fake mold, just like it will go when you glue it up. Do a dry run. Get it just like you will want it, with about a half inch of overlap of the new gasket with the fabric cuff. The point of the "pooch" in the balloon above the fabric is to help hold the new gasket in place. Get it just right, and so that it is stable. This is key. If you try and rush it and put glue on it, you will probably make a mess of it. At that point you will have fucked it up.
So far you haven't, so here's the Zen moment. With the gasket in the full, dry mock up, simply roll up the 1/2 inch overlap against the shaft of the balloon hand just like the rim of a condom. Now, the part of the gasket that will soon be glued to the fabric is facing you. You may need a bit (a little bit) of tape to keep the rolled up section even and stable. Again, a bit of a pooch in the balloon will help hold this.
Take a breath. Apply Aquaseal to both the fabric and the rolled up section of gasket. At this point, you can easily get caught up in your euphoria that this is actually going to work and the various Aquaseal techniques and the glue fumes. Persevere. It really doesn't matter whether you put glue on both the fabric and gasket or only one of them. Cotol is unnnecessary, because you are going to be so sparing with your glue application that there will be no gaps, nor drips. You can do it!
Apply a thin film of glue to both surfaces, and... Roll the glued up, inside-out gasket down onto the fabric cuff. Push down on and around the outline of the glue joint with your finger, ensuring that there are no gaps. Position the whole thing in a suitable drying position. I like the balloon arm and gasket to be in an upright position. Watch your new creation for the first 30 minutes. There will be an occasional slow drip. Take care of these little bastards with a paper towel.
You can do it.
PM me if this explanation is not clear enough. (It probably isn't)