The usual cause is from someone working on a tank module (pump or filter) and not refitting it correctly. The seal will only fit one way up on the tank port lip. Check whether the existing seal is mechanically OK but misfitted. The seals themselves are fairly robust and it may not require replacement.
This might help:
https://the75andztclub.co.uk/forum/s...ead.php?t=9108
You need just the port seal info.
TC