Advice on old Majestic ZC FP install needed

[Reluctantreno]

I've identified our wood-burning fireplace as a Majestic WM36, installed in the 1980s. As you can see in the pic, it is enclosed in wall-to-wall MDF cabinetry. With strong rain and wind we were getting some water on top of the cabinets. We re-caulked the storm collar on the roof to hopefully end that issue. I also cut out a section of the ceiling to get rid of what was somewhat moldy drywall. The chimney was wrapped with fiberglass insulation and then the flexible plywood (black) in the final pic. I tossed out the insulation as it was dirty, and can now see where the water was entering through the gap between the firestop and chimney. A couple of questions as I contemplate putting this all back together: Can and/or should I seal that gap to prevent further leaks? I'm thinking that would prevent the original issue from reoccurring, but then I might just have water sitting in my ceiling. There are also gaps around the firestop sides. Problem? I'm also wondering if I can/should just leave the chimney exposed rather than re-wrapping with insulation. Finally, we have always had a heck of a time getting a good updraft in this fireplace. Is there anything I should look at in that regard while I've got things exposed? Thanks for any advice.

 

[begreen]

The most important thing is to stop the water from entering in the first place. By the time it's reached the firestop, sealing there is just going to allow it to puddle and spread across the ceiling.

Is this insulation wrap approved for the chimney pipe being used?