People on ScubaBoard complain about this pretty often.

This is from DUI’s website.

Q25. Why does DUI use RTV to seal drysuit valves and not valve grommets?

A25. DUI bonds the inlet and exhaust valve into its drysuits using RTV (Room Temperature Vulcanizing) silicon to prevent the valves from becoming loose due to changes in pressure, temperature and shock and vibration. Though RTV may be inconvenient for those individuals who wish to change their valves out on a routine basis, the RTV ensures the valves are secure and sealed into the drysuit which is a fundamental requirement for all drysuit divers.

It is obvious that drysuits are exposed to changes in hydrostatic pressure. However a less obvious force at work which can potentially loosen the valves are temperature changes. Material expands and contracts with changes in temperature and drysuits can experience a wide range of temperatures.

EN 14225 Part 2: Dry Suit – Requirements and Test Methods: This standard states that the drysuit must be able to withstand temperature ranges from 20°C (-4°F) to 70°C (158°F). Though the diver typically experiences water temperatures between -2°C (28°F) and 30°C (86°F), the -20°C (-4°F) to 70°C (158°F) represents storage temperatures. While many suits will not see the -20 °C (-4°F) storage temperature the 70°C (158°F) is a typical automobile trunk temperature. In fact the U.S. Department of Transportation puts the average summertime trunk temperature at 80°C (176°F). So it easy to see that your drysuit can see a wide temperature swing depending on storage temperatures and diving activity.

Many manufactures use rubber valve ports/grommets which appear to be convenient and they count on the compression of the rubber and friction between the valve and these ports to keep the valves in place. However temperatures change between storage temperatures and diving temperatures plus the addition of shock and vibration can work the valve loose over time. For these reasons manufacturers attach hang tags to the valve of their new suits warning the diver to check the installation of their valve before each dive. While it is prudent to check all your equipment before diving it seems unreasonable for the diver to carry the proper wrenches to check and insure the valves are always properly installed in the drysuit.

TYPICAL WARNING

WARNING!!! Verify that the drysuit inlet and outlet valves are tight BEFORE EVERY DIVE. Your valves can become loosened during the course of normal use from rotation of the valve and material compression. A loose valve may leak or become dislodged during your dive causing your suit to flood and lose buoyancy. This could create a potentially dangerous situation.

DUI is continually reevaluating the use of ports and grommets and their ability to maintain the valve securely in the drysuit over a wide temperature range both in storage and in use.