O-rings (linked below) could be involved in the water seal, but the error light is usually going to mean the system is detecting an operational issue that you might want to check the manual or troubleshoot for.
Union O-rings:
https://www.discountsaltpool.com/circupool-core-small-o-ring-set-union-connections
Controller O-ring:
https://www.discountsaltpool.com/circupool-core-large-o-ring-control-connection