A swollen or soft seal can suggest fluid incompatibility. A hard, cracked or brittle part can suggest heat or chemical damage. The same part can suffer both. Its appearance is a starting point, not a material test.
Write down every fluid the seal has seen. Include product, cleaning chemicals, rinse and steam, with concentration, temperature and exposure time. Note any recent change in recipe, cleaning cycle or operating pressure. Keep the container label and the material specification if available.
Look at where the damage sits. Is it confined to the elastomer near hot seal faces, or is the whole part affected? Are the faces showing heavy wear or local thermal damage? Was the flush working? Local heat at the faces can expose an elastomer to more than the temperature shown on the main process display.
Do not identify the compound by colour and do not substitute one solely from a compatibility table at room temperature. Ask for the original specification and, where required, the compound and approval records. If the failed part is badly changed, retain it for assessment alongside an unused sample. We can then compare the evidence with the real duty before choosing a replacement.
Related: FFKM Chemical Compatibility, FFKM vs FKM Comparison and Why is my O ring flattened and leaking after heat or cleaning cycles?.