When o-rings fail its commonly one of the issues, they're the wrong size, impromper installation, excessive pressure, expansion rupture and chemical degradation.
Piston Ring Install Guide: Clocking and Gap Orientation
A Guide to common O-Ring failures – Totally Seals
8 Reasons for Mechanical Seal Failure
5 Reasons O-Rings Fail and How to Prevent Them, Seals
How to Diagnose a Damaged O-Ring and Determine the Root Cause
Why O-rings Fail (and how to prevent it) - Techno Ad
A Guide to common O-Ring failures – Totally Seals
Solving the Common Causes of O-ring Failure
O Ring Failure Guide - Abrasion / Extrusion / Compression set
Common Reasons Why O-Ring Fails