DIESEL FUEL TANK LEAK

Some boats you can run both motors off of one side, but the boat has to have the valves in order to do so. I'm guessing yours probably does not and one engine draws and returns to one tank, and the other draws and returns to the other tank. If you replace the tank, plan on doing both tanks as the port tank most likely is not far behind the starboard tank. No way to repair existing tank, it will just leak again.

You can get someone to add the necessary fuel lines and valves to run both engines off one tank. This is a nice option to have as a back up solution for many fuel issues. As Capt J states you have to plumb both the supply and return lines. I would recommend you get a professional to do the work. Running both engines off one tank will continually create a balance problem plus you will be carrying extra weight for balance. I second what Capt J said about the other tank, it may be ready to give way. There are bilge sensors to detect oil in the bilge water to prevent overboard discharge.

And what is the point of spending any money to put a water bladder in a bad fuel tank??? The other fuel tank isn't going to be in any better condition and the pickup in 1 tank isn't large enough to supply both engines. The boat will always list depending on how much fuel you add or use from the port tank. Why couldn't you remove the floor and take the tank right out of the salon door and put it in that way? I've seen the old tanks cut out and a couple of the same size tanks but shorter put in and linked together. Their has to be a much easier way to do the job properly.

A repair like you propose makes the resale value drop to almost nothing. That may or may not matter for your circumstances, but something to consider.
Water ballast is an empty solution, an inverter solution with more batteries are better than fluid ballast and better for resale.
Keep on looking for contractors who can offer a better solution.

Your insurance company may not appreciate non factory fuel mods also.

Huckins Yacht just did the same job on a 40+ Maxum for $13k including tanks.

Which is what I guess this job would cost at the right yard. $15k or less for both tanks.

Do you know how difficult it is to cut out the baffles out while the tank is in the boat, let alone out of the boat!? You will never get it all out , and it will be to sharp where you cut no matter what. Pop goes the water bag...it's a waist of money.
Drain/pump/clean out all the fuel. Plug all the welded in fuel fittings, patch the leak with marine tex or silicone , what ever, and fill it with water. There you have your counter weight back....cap off the deck fill to with a ''Water'' cap.
Sounds like you found where it's leaking ? You may be able to weld on a piece of aluminum to repair the leak...but you really need to get to the tank to do that. The entire tank may not be all bad.

Years ago I repaired my Father's 400 gallon steel fuel tank on a 55' Pacemaker MY. The tank was under the master stateroom king bed aft just sitting on the bottom of the boat and when you ran the boat , or she had some water in her( Lol was a wood boat) The water over the years rusted areas of the bottom and sides out to where the tank would weep out some fuel. The rust only came up the tank around 2 or 3 inches all around. The rest of the tank was still fine.
I/ We were able to clean out the tank flip it over in the state room and I welded on a 12ga. 304 Stainless Steel bottom pan 8'' deep to the ''good steel'' on the old tank . Problem solved. It out lasted the boat, btw.

Boat builders, btw, put all that crap into the hull/boat before they lower the deck and cabin on. It's quick and easy for them. They don't try to cram things in when the boat is entirely assembled. Which is what we have to deal with as owners.

Check cleared, warrantee is over....they( the boat builders) don't give a Toot! Production boat builders only build them so good....
Insurance won't pay a dime..btw.

Aluminum or steel ? You should find out, so you know..not what others tell you. Put a magnet to the tank ...if it sticks you got steel, if not it's aluminum or 300 series stainless steel which I'm almost sure it is not.

It's aluminum. The other tank is not far behind also.
Just it's age proved it was on borrowed time these last several years.

I'm sorry most responses are negative. A few of us are/were in the marine service companies.
Done correctly to protect your investment and have any liability coverage; is to correctly replace the tanks.

Good luck.

Our glass tanks will be 41 next month.