Seals fail quietly. There is no warning light for a gasket that has taken a permanent set; the case simply stops keeping water out, usually discovered when something inside is already wet. Learning to read the early signs changes that from a surprise into scheduled maintenance.
The Stages of Seal Ageing
| Stage | What is happening | What you notice |
|---|---|---|
| Compression set | The gasket stops springing back to full height | Lid closes with less resistance; seal looks flattened |
| Loss of resilience | Material stiffens or softens with age and temperature cycling | Seal feels hard, or tacky and soft |
| Surface cracking | Ozone, UV and age break down the surface | Fine cracks, especially at corners and bends |
| Material breakdown | Chunking, tearing, permanent deformation | Visible damage; seal no longer sits in its groove |
Compression set is the one to catch. By the time the material cracks, the case has usually been leaking for a while.
Three Checks That Take a Minute
- The paper test. Close the lid on a strip of paper at several points around the perimeter and pull. Resistance should feel even all the way round; a spot where the paper slides out freely marks a weak area.
- Press and release. Press the gasket with a finger. It should spring back promptly. Slow recovery means compression set.
- Look at the corners. Corners are where the seal is stretched and where seating is hardest, so they age first.
Simple Habits That Extend Seal Life
- Store cases latched loosely or unlatched during long storage, so the gasket is not held compressed for months.
- Keep the seal clean — grit and salt abrade the sealing surface and hold moisture against it.
- Rinse off salt and chemicals after coastal or industrial exposure.
- Keep the gasket out of direct sun where possible; UV is hard on most elastomers.
- Avoid solvents unless confirmed compatible with the gasket material.
When to Replace
Replace on condition, not on a calendar. Clear triggers are: the paper test showing weak spots, visible cracking or chunking, a seal that no longer sits correctly in its groove, or any confirmed water ingress. Replacing a gasket is inexpensive compared with the damage a leak causes, so when in doubt, replace.
Material choice matters when you do — the trade-offs between EPDM, silicone and closed-cell foam are set out in our guide to gasket and O-ring materials. And if a seal has failed on a case that is otherwise sound, check our article on repair and spare parts for what else is worth replacing at the same time.