Reddit reviews Dicor Non Leveling Non Sag Lap Sealant 551LSW

Do you have a picture (peferably inside and out), and have you been able to locate the specific location of the leaks? Is there rust on the metal side of the seam?

If no significant rust, this stuff is great for sealing leaks. You want the non-leveling type as the leveling kind is for use on a flat surface like a roof.

If the seam gap is big, first plug it with butyl tape then the non-sag sealant.

If the whole seam around the perimeter of the roof is leaking, I'd first clean it really well (one of the most critical parts of effectively applying sealant), then pack a thin line of butyl in there, then seal it off with the non-sag sealant. Treating only from the exterior should fix it, but if you have direct access to the seam from the inside, a bead of sealant there too won't hurt you.

I've done basically that process a couple times to seal rv leaks, and it works very well. Gotta have super clean surfaces, though. Worth buying a bottle of alcohol and going over it with that before applying butyl/sealant just to be sure, once you've cleaned/scraped any crud off.

Kudos for not using silicone; you'd be in a world of hurt if you'd done that.

Edit to add: I agree with u/crockett5 in the Q&A thread, we need photos and to know if there are any holes in the fiberglass and/or metal and what the seam looks like to find the best fix. Do NOT plug metal or fiberglass holes with butyl/sealant. They are for seams only, and while it might solve your problem in the short term, you'll probably be in a world of hurt a few months down the line

Also, post stalked you, and from the far away shots, it kinda looks like there might be a black rubber strip around the seam? Is that true?