Lewmar Bridge Hatch

Why wouldn't you just replace the gasket?

I can't speak to the specific caulk used but even if it's 52 million it's not too difficult to remove intact. Start with several long taper wedges, usually a hardwood works best, working on a corner and out as you begin lifting the flange. Slow and steady pressure will eventually get enough gap to work with, once you've got a gap started, use a piece of Dacron fishing line or the newer braids, as a "saw" and slice the caulk under the flange working around the perimeter as it releases.

There is a second formula of de-bond for 5200 woes. The first version worked well for me on one project.
Patience is a must.

Judicious use of a heat gun really works a treat on sealant. I learned that embarrassingly late in life.

Tashmoo, I had to do the foredeck hatch on my 43'. I have to now do the one in the hardtop as well. They are leaking around the flange as you described. When I pulled the foredeck hatch it was not too bad. I removed the screws then used a utility knife to "cut" the caulk from the outside. Then I used a sharpened putty knife and some hard wood wedges. Was able to get putty knife under a corner, and pry it up enough to push a hardwood wedge in. Then I tapped a succession of about 4 wedges going around, removing and replacing, until the hatch just broke lose. Not a big deal.

What condition was the frame when it broke loose?
Not to dump on your event, but 3M 5200 is a PIA to break loose. Some other bonding / sealants are just as mean. If your frame was re-usable, then great & FM.

The frame was in fine condition. Rebedded it with boatlife caulk and have had no trouble in 2 seasons. I don't think it was bedded with 5200 but regardless, using small hardwood wedges tapped in with a hammer is a great way to slowly apply even pressure without mangling the hatch. Beats the heck out of using a prybar.

Prybar??? Never thought of that. We just use detonating cord..

It is rare to re-use a hatch in our area, by the time it needs to be re-sealed, it's usually already eaten up by the sun and salt. Our shop always installs a new hatch.
With lead time (4 weeks) , Bomar will make a dis-continued hatches for older boats.

The hatch was in good condition when removed, it was a pretty heavy unit. I tried to find an off the shelf replacement to no joy. I did check with bomar on a replacement as the paint was failing on mine and the lens needed rebedding. But they wanted about $1200 and quoted a 6 week lead time. So I elected to strip the paint, repaint it with rattle can "epoxy appliance paint" and rebed the lens. Took a few hours but seems to be holding up well. No replacement for new obviously but with this boat I've had to pick my battles.

As to the det cord, I never thought of that. I like it...