Cockpit Leak

Air tight?? in a boat??
That's funny..

If you don't have draining gutters, you can pull the decks up and install gaskets.
Or am I missing your point??

After your sure your gutter drains are clear (if you have them) and want to tighten up the seams;
Tape off the seam line on both sides and fill the cracks with 3M 4000. Fillet with gloved fingers and pull the tapes up quickly.

That is such a great design on the drawing board. Can you imagine the designers at Silverton when they came up with that? I sort of get it but there is no way to keep water out of that. Sure will be awesome if someone ever re-powers.
By the looks of your engine room, you are on top of maintenance.

Now for your question, not being sure how the cockpit cover sits, I imagine the edge is molded over and sits in a gutter? If so, how many drain holes, limber holes, are in that gutter? That is a large rim with water pouring over every edge. I may be inclined to place more drain holes in the gutter and make sure that the drain hoses that connect to those drains run downhill for sure.

In this pic, you can see the drains. One under the transom door in the corner.
Are these clear?

Looking up from below, Should be good sized gutters.

Ah, but from here, light coming in. I can see where wash water from a hose can easily come in here.
Looks like something in the gap holding the lid/deck up.
What is that L bracket doing their also?

Compared to the bottom of the saloon door, I would say that corner is up.

Been thinking about this.

Lets go over this picture again;

A is a deck support to keep the deck rigid in front of the saloon door.
B is a spacer that supports the deck also and keeps the mounting bolts from pulling the deck to far down. These are all around the mounting flange.

I have no idea what C is.
Could be something keeping your deck from coming down correctly and letting that light (water) in???

First my caulk idea is not going to work. Scratch that.
How bout closed foam strips of the correct thickness.
Pushed in place from the inside of the ER just along that first edge before the gutter.
Looks like split pool noodles could fit in that gap.

Based on the previous photos, I suspect that most of the water finds its way inside the e/r from around the borders of the large cockpit cover, rather than the hatch going down inside the e/r.
My boat has a very similar arrangement, except that the whole cockpit floor is not even screwed in place (as this one seems to be), but it's just hinged on the aft side, with closed foam strips all around it to avoid rain and washing water seeping inside the e/r.
Theoretically, that would allow an even faster opening of the whole cockpit for working more comfortably inside the e/r.
But in practice, lifting such large and heavy panel is a helluva job even if hinged - and unnecessary for normal maintenance, anyway.
So, long story short, I went as far as throwing away the foam strips and caulk all the border for good.
The pro is that now not a single drop of water can even reach the external supporting the large cockpit cover.
The con is that for lifting the floor, I'll have to strip the caulking first. But optimist as I am, I hope it will take many years before needing to pull the engines out...

That said, I don't think this would be feasible in the OP boat, for two reasons.
First, my cockpit floor has teak above it, so the caulking all around it actually fits nicely and seamlessly.
Second, the teak fits much more tightly with the superstructure around it, so the caulking gap is just a couple of millimiters larger than the normal caulking between each plank.
OTOH, it would take quite a lot of sealant to fill all the borders in the OP boat, judging from the pics.
Bottom line, your closed foam strips idea (pressing them inside the border as tightly as possible) is probably the best idea.

I see two drain holes in the access hatch with typical closed foam stripping.
Closed foam stripping around the entire cockpit floor cover is a reasonable idea, caulking the perimeter sounds like a last ditch effort.
I see two drain holes for the entire perimeter, add more holes and tee them into the existing overboard hosing, as I already mentioned, be sure all hosing runs downhill. Ask me how I know that

In a sense you are correct, but I didn't explain the whole rationale behind that, in my previous post.
In fact, it's not like I had torrents of water inside the e/r before.
Just a few drops, and only after I insisted a bit too much with the hose, when washing the cockpit.
So, caulking the whole perimeter was arguably OTT, if it were for water alone.
But on top of fitting nicely with the teak floor, the caulking also made the cockpit much cleaner, because the perimeter around the floor used to be a hard to reach dirt trap before.
But as I said, probably it isn't the best route for the OP boat, with that wide-ish groove around the perimeter.
Which if nothing else, I guess is easier to clean than my very narrow one was before caulking it!

That's it! Time to buy a new boat.

All the best in your quest for engine room water mitigation. Have you found Ovation/Silverton owner's groups on other online platforms that may be able to shed some light on your situation?

I was thinking pool noodles sliced length ways to fit.
https://en.wikipedia.org/wiki/Pool_noodle

Or if not into colors, the proper tool would be something like this;
https://www.lowes.com/pd/M-D-Expandable-Foam-Weatherstrip-1-2-in-x-1-2-in-x-20-ft-E/1002926160