I've heard lots of advice about repairing gaskets, but after repairing about 10 gaskets on my own and setting on the best way to do it I thought I'd take some pictures and post instructions on how to do it.
The best option for Drysuit gasket repair is to send it back to the manufacturer. The biggest problem with that is one of time. Most manufacturers cannot turn around a repair in the time span I would need since I paddle at least once a week including in the winter. I simply cannot go without my drysuit for a week or a month or more. I have sent it out to other drysuit repair places that repaire diving suits but I didn't like the rubber gaskets they used, they were heavy and rubbery not smooth and latex like.
The first thing you should do is order the gaskets, I ussually get mine from NRS, but if you have a friend who has a boat or outfitting store they are much cheaper if you can buy them in bulk instead of onesy-twosy.
Make sure the gasket is your size, there
are ussually two sizes for neck and wrist gaskets, ankle gaskets only come
in one size. Try to match the sizes with whats currently on the suit,
you can always trim it later, so if you err, err too small not too large.
Clip the old gasket off leaving about 1 inch of old gasket on the ends.
Create an outline of the gasket on a piece of thick minicell. Start by punching the knife right through the minicell and cut out the circle without cutting anywhere else outside the circle. The pieces should fit firmly together. Mark with arrows at some point on the circle so you know how to make it line up.
Stretch the Drysuit around the minicell, it should have a really snug fit. Clean around the outside with cotocol and clean the gasket with cotocol as well. Make sure the seam lines up with the arrow
Thin the aquaseal with cotocol to make it more flexible. Coat the outside of the gasket, then stretch the gasket over top. I ussually use tape to hold the gasket in place then stretch your piece of minicell over the top with the arrow pointing towards the seam in the drysuit. If you spill a little around, thats OK you can remove it later.
The final results, you can put a bead of aquaseal around the seam on the inside if you're paranoid, but I don't ussually. The excess Aquaseal can be peeled off the surface of the gasket carefully. Trim the gasket carefully with a pair of scissors to the correct size. Remember err on the too small side.
Rips in the Drysuit can be repaired with Drybag repair kits, patch both sides and use lots of aquaseal.
Good Luck
Karl