Unlike the others I'm not happy with my neoprene neck seal. My suit was an ebay special (but brand new) Bare Trilam HD. It has fold under neoprene neck and wrist seals.
The wrist seals are just about ok unless I do so extreme excursions with my hands/wrists.
However the neck is a different story. I've done a grand total of 5 drysuit dives ( 3 outdoors and 2 pool dives), and every time I've got wet, primarily water running down my back. The problem seems to have become worse as the seal has stretched a bit.
Note that I didn't do anything to overstretch the seal, and I followed the donning instructions to the letter.
In particular I notice that when I tip my head forward (usually to look at my SPG, which is clipped to the left D ring on my Transpac), I get a shot of water down the back of my neck.
I've come to the conclusion that skinny people and these seals don't seem to mix too well (I'm 6' and 175 lbs). At the moment the only things I can think of are either changing it out for a latex seal or cutting a chunk out of the neck seal and rebonding it to tighten it up. I've read of some people using bungee or shock cord to tighten the seal, but that seems a bit dangerous to me (if the cord fails).
Any comments gratefully received.