Hi Tracy,
Thanks for that. The boat is 'new to me', so everything is a discovery.
Probably a made up Flexi is better long term.
I'll measure the pipe next time I'm at the boat.
I've been working on some other engine issues and although the leak is currently small, I just wanted to stop it with the least extra drama while I'm running the motor and checking the other bigger issues are resolved.
I thought I read somewhere in the BSS guidelines about having solid copper piping between joints (could have been across injectors) and maybe that was interpreted for the pump to filter connection.
Truth is, it could be many reasons, but I appreciate all the best practice advice from you and Tony, which will definitely be really helpful to make things better as they are addressed.