People used to believe that heavier objects fell faster than lighter objects (if you still think this, don't admit to it)...
Petryk.... play nice...
Ok, I'm a chemist but I haven't professionally worked as a chemist for around 10 yrs. So don't ask me too many questions and if you do expect a lot of "I do not recall...".
Latex is the sap from the rubber trees. It can also be produced synthetically. Latex is used to make natural rubber. Uncured natural rubber is sticky, not very elastic because it easily deforms... Sound familiar?
*say goop*. You usually cure rubber through a vulcanization process. At the molecular level, what the vulcanization process does is create crosslinking bonds between the long chain molecules of rubber. The bonds usually use something like sulfur atoms.
The reason why rubber becomes stable and elastic when vulcanized is because the crosslinking bonds prevent the long molecular chains from moving independently from each other. You can apply stress and deform the structure, but the crosslinking will bring back the chain molecules to its original position once stress is relieved. If the crosslinking sulfur bonds are suddenly broken the nice elastic and stable rubber returns to goop.
There are many reasons why the sulfur bonds could break. Radiation with particles that have a higher energy than the strength of the bonds could break it (eg UV from the sun). Solvents, chemical reactions with substances that bond with sulfur, the presence of catalytic agents that enable a reaction with other substances that would otherwise have no effect on rubber, etc.
Keep in mind that in the explanation above I am grossly oversimplifying. There are additives, stabilizers, patented formulas and procedures to modify the properties of cured rubber. By modifying many combinations of different properties you can regulate the likelihood to return to goop. So just as in many other things, there are different grades of rubber. Maybe adding lead has a stabilizing effect, but it could also has a toxic effect when in contact to the skin. Maybe a higher rubber grade requires a more expensive and careful manufacturing procedure like doing better longer mixing of ingredients in the vat to avoid creating portions of the rubber batch that don't have enough sulfur or have too little of stabilizer x.
Current chemical knowledge is more than enough to allow rubber producers to come up with safe and stable seals for drysuits. It will not be eternal, but it should be reliable. If it is not stable within a reasonable amount of time then you have a defective rubber seal. If there are lots of people experiencing this failure, then it is most likely that a large defective batch was distributed to drysuit manufacturers, or the manufacturers are simply not specifying the correct grade of rubber to fulfill the expectations of the end consumers. And then there's always the superior silicone alternatives.
It is the same situation that you would find with metals and metal properties and grades. As an end consumer you would not expect your car's suspension springs to break up in the 3rd year of the car's life because of excessive corrosion. If they do it's either a defect or the manufacturer needs to tell the user to change springs every 2 years.
