[RF5BPilot]

Is a GFCI breaker on an electrical panel more sensitive than a GFCI outlet?

Problem:
A GFCI breaker in an electrical panel has started tripping. It runs to an outlet in the yard which has powered a pump in a water feature for 10 years or so.

When I plug one of the other, smaller pumps into the same outlet, the breaker doesn't trip.

So -- it seems obvious that it's the pump.

But -- when I run an extension cord to the same pump and plug it into either a regular outlet or a GFCI outlet -- it runs fine. Nothing trips. So, although the pump has started tripping the panel GFCI, it doesn't trip a regular outlet or an outlet with a GFCI.

I thought (hoped) maybe the breaker had an issue. Replaced it. Stayed the same.

So, it's probably the pump or its electrical cord. But the issue has to be minuscule if it won't trip a GFCI outlet.

Suggestions/Ideas?

(My next step is to replace the pump. But it's large, expensive, will be a significant chore to replace and I don't want to get into it if there's something else I should be testing/checking/etc. first.)

Thanks.