I'm tall but rather small-boned, and my XL drysuit has always been marginal on the wrist and neck seals, which are neoprene with a smooth lining, rather than the more common latex. This is much more comfortable, and not prone to perishing, but isn't quite as stretchy. The rest of the drysuit is the normal gore-tex fabric (and a little baggy even over winter layers).
I got away with the marginally loose fit on the wrists by using some strips of latex wrist seal over the top as rubber bands. Since losing a bit of weight even this doesn't work and all the seals leak noticeably. They're in good condition; it's clearly just looseness. A rather silly swim on Sunday demonstrated that it doesn't keep me as dry as it should.
So what I'd like to do is cut a small V of material out of each seal and rejoin it. The existing seals clearly have a join in them so it must be possible with the right materials. This join appears to be stitched and glued and have a reinforcing/sealing tape glued over the top, as seen in the photos:
Interestingly the tape is only present over the seams that stretch round the wrists/neck, and not on the other neoprene-to-neoprene seams