Leaking shower & rotted subfloor 53MY

Hi. My sister & I recently inherited our parents 1973 53MY. Our parents owned it for 25 years. We are cleaning it up and potentially getting it ready for sale. We pulled out the carpet my parents installed when they purchased it, and discovered an issue in the master & mid heads. The shower must have leaked for awhile, and the flooring underneath is rotted. My dad evidently tried to fix the leaking and replaced a portion of the subfloor in the middle head closest to the shower. The master still has the original linoleum and trim, but the floor underneath closest to the shower feels soft. We haven’t pulled it up to take a closer look. I’m sure others have dealt with this, but my searching of the forum didn’t find anything. We’re looking for advice on finding and fixing the leaky shower and the best way to deal with the rotten subfloor. Thanks!

I also have a 53MY and the Jack-n-Jill shower leaks. Do you know what your father did to stop the leaks? Looking forward to responses to your post, hoping I can learn something.
Good luck.

There are numerous areas in the single shower and in the adjoining showers. I found the biggest leak in the inspection plate facing the starboard bulkhead. I took it completely out and apart, dried it, sealed all the wood edges with silicone, then I embedded the metal trim in silicone and screwed it back into the cover/hatch. Then I Applied a bead of 4200 between the metal and the shower wall and screwed it down tight. That was five years ago and I have had zero leaks sense. The second location is in the screw heads that mount the shower pan. I removed all of them and put a bead of 4200 behind the shower pan where I could. I replaced all the screws and embedded those in 4200 as well. Then I ran a bead of silicone around the entire edge. No leaks from there in the same five-year period. The last location is in the drain hole it’s self. Mine did not have any leaks so I am unable to inform you how to repair that. The last location is the shower door frames themselves. I clean them with acetone and applied a thin coat of clear silicone caulking to any area that would allow moisture to go through. It’s not that big of a job should only take you a few hours to do the shower completely. Good luck

my boat came with a piece of rubber along the bottom of each shower door running the width of the opening, this makes any water that hits the door go into the shower pan and not run down the door frame and leak