Given that you have ruled out everything else and the leak has stopped, I don't think this is a crazy idea either.
At the same time, if this was the problem, then it might be a good idea to remove the cap to check on its condition and the integrity of the gasket and fasteners. If your boat is using screws to hold the cap down, you might be wise to replace them with bolts and fender washers. If the cap seems solid with no cracks or damage you might get away with replacing the fasteners without removing the cap but, in my view, if you go so far as to remove the fasteners, checking out the cap and gasket as well as the hardware and tether would seem prudent.
There have been cases reported where the centerboard has actually cracked the cap when the boat was launched with the tether slack.

Graham Stewart
Agile 76

On Wed, Dec 20, 2023 at 10:37 AM Peter Nyberg <peter at sunnybeeches.com>
wrote:

> Reuben,
>
> That doesn't sound like a crazy idea to me...
>
> Peter Nyberg
> Coventry, CT
> s/v Silverheels (1988/2016)
>
> > On 2023-12-20, at 08:56:56 EST, Reuben Mezrich wrote:
> >
> > In casting about for possible causes of the rather large (~2ft, to the
> top of
> > the settee) flood into my boat I started wondering about the swing
> keel...in
> > particular, what happens when the boat lies on the ground? The day of my
> flood
> > had a particularly low tide, in part because of winds pushing water out
> of the
> > bay. I suspect my boat spent some time lying on the mud at the bottom of
> my slip
> > and I'm wondering if that might have pushed the swing keel up into the
> top of
> > the centerboard trunk, possibly flexing it and causing a leak. Given the
> 50 or
> > so screws that hold the top down that is unlikely but..... The boat is
> floating
> > now and I can't find a leak (thru hulls are OK and I don't see water on
> top of
> > the
> > centerboard trunk). ...so I"m grasping at straws.
> > --Reuben
> > Reuben Mezrich
> > cell: 410-499-8922
> > Pelican Cove in Sarasota and Back Bay, Boston
> >
> >
> >
>
>