I am disappointed that my Bomber Gear dry-top neck gasket is too loose after just 2 years of use. I trimmed it down to "comfort level" when I bought it. Stretching and time have caused it to become loose to the point of ineffectiveness. I now put on my NRS Mystery storm hood first, then put on the drytop so the gasket fits more snuggly around the neck-portion of the storm hood.
I just received a new dry-suit and have tried a different approach. I have left a few more rings on the neck gasket so that it is a bit uncomfortable. I sat in the house with the suit on for an hour and thought: "this is just still too tight." Neck veins are bulging, pressure in the skull and eyes etc. So, I pushed the gasket down as far as I could on my neck, to the point that the gasket is INVERTED and doubled under itself, almost down to the collarbone. Even though the gasket is very tight, I was very comfortable for an hour with the gasket pushed down lower in this way.
Apparently, pushing the gasket down further, causes less interference in blood flow through the neck. Hopefully, this will get me at least five years of use out of this new gasket.
In my experience,
anything made of latex has a good life of about 3 years. Latex gloves, even in a sealed box, become near worthless after this amount of time. My last neck gasket made it 2 years before I could see degredation. One thing I found is that my “5 o’clock shadow” is hard on the gasket. I was thinking that maybe a silk bag over my head while I am stretching the gasket over my noggin might help.
I think…
…it’s less stressfull on gaskets to slip a finger or two under them and sorta walk the gasket over the larger body parts rather than doing a punch through. In fact getting my heels through ankle gaskets pretty much requires this technique. Ankle gaskets hang so bad on my heels that I am afraid I will rip them if I just try to pull them on.
Most of my gasketed stuff is BomberGear but I have one pair of Kokatat dry pants. The BG gaskets are thinner and softer than the Kokatat. This makes them more comfortable but I imagine it also gives them a shorter lifespan.
I have low blood pressure and it takes very little constriction to cause my feet to fall asleep so I like the softer BG gaskets. I’m sure a tight neck gasket would have me seeing stars in minutes. 
…Mike
To keep using a stretched gasket…
Great marks to that Bomber Gear gasket for lasting so long that it stretched out major league without ever tearing - if you want ot get it replaced you may want to look up a good scuba shop.
But - apparently some cold water divers just cut the gaslet loose enough that they actually wear it folded over double to start with. Stays dry and doesn’t challenge circulation.
Typical degredation
When a latex seal gets loose like that, it indicates that it's degraded from UV, skin oil, sunscreen, etc. Trimming it less wouldn't make it last much longer, since it will start coming apart soon.
Your tip about pushing the seal down is interesting. As long as you don't need neck protection from cold water, it should work fine. I'll have to try it when the conditions are right.
Very clever. Your experience shows why
I am reluctant to trim gaskets. Planned stretching gives a gasket which is comfortable, and which (in my experience) can go up to five years without ever being too loose.
I have never trimmed a gasket. However, if you are in a hurry, trimming is just fine.