A watch gasket is a small seal placed between parts of the case. You may find one around the case back, crystal, crown, or pushers. Its job is simple: help close the tiny paths where moisture, dust, and dirt could enter.
A gasket supports water resistance
A gasket is usually made from a flexible material such as rubber or a synthetic compound. When the case is closed, the gasket is compressed between two surfaces. That pressure helps form a seal.
The gasket is important, but it does not create water resistance by itself. The case, crystal, crown, pushers, and case back all have to work together. A damaged part, loose crown, or poorly seated gasket can compromise the whole system.
Why watch gaskets age
Heat, sweat, dirt, chemicals, and time can harden or deform a gasket. Seiko notes that water resistance is not permanent and can be affected by aging gaskets or watch parts deformed by shock. That is why an old depth rating should not be treated as a current guarantee.
Opening a case can also disturb the seal. After a battery change, service, or case opening, the gasket should be inspected and the watch should be pressure-tested if water resistance matters.
What owners should do
- Keep the crown fully closed before the watch gets wet.
- Do not operate the crown or pushers while the watch is wet unless the manufacturer explicitly allows it.
- Avoid solvents, sprays, and harsh cleaners around the case.
- Ask for a pressure test after service or before relying on an older watch in water.
A gasket is inexpensive compared with the movement it protects, but its condition cannot be judged from the dial. If you see condensation under the crystal, keep the watch away from further moisture and have it inspected promptly.
For the bigger picture, read what water resistance actually means.
Source: Seiko water-resistance guidance.