I'm told most poly tank builders these days weld the seams outside AND inside, whereas earlier in some cases, only the outside seams were welded and this may have contributed to problems. Suspect the technology also a bit more advanced. I was turned on to the Maine poly fabricator by a friend who works at a boatyard in Maine, no affiliation, he says the guy's tanks are regularly installed in Sport-fish that'll go +40 kts in high seas and no failures. Apparently Lyman Morse has been putting his poly tanks in their high-end sailboats for years. FWIW, the poly tank has a lifetime guaranty, whatever that means. Nevertheless, I'm fairly certain 3/8" plastic will outlive 1/8" aluminum in the marine environment, but I'm confident 1/8" alum if kept dry will last a long, long time too.

I would only paint the outside (and bottom) of the tank to resist any kind of moisture / corrosion ... just a thought;

I can easily drill for new pick-ups & fittings, in place, but best would be to weld a boss or coupler to the tank for new fittings, and thread fittings with tubes attached to them. And to do any welding, best to have the tank at the Shop. And if I do that, I might as well replace the darn thing, a new one doesn't cost that much. It's 26 years old, who knows how much longer it'll last. One thing I do know ... If I do all this work to the existing tank, it most certainly will fail this year ! Easier to remove the access plates, bring them to the welder and have the boss / fittings / tubes installed in them. But they'll just be in the way whenever I want to remove the access plate and clean the tank. My existing access plate leaks vapor slightly (but no liquid), one of the fasteners is stripped, it's just a self-taper into thin skin, I've wanted to replace it for years. Have you seen these access plates > www.seabuilt.com ? Look very nice, but $150. And I'd rather not have the pick-up anywhere near the return, so if I get a second access plate, another $150 and more work, and at that point I might as well get a new tank.

I don't think the mounting pads are worn out, but I really can't say what is happening until I get the tank out, which I have not ever done. The tank doesn't have flanges or tabs to secure it, it is locked in by framing. Not sure what it is sitting on.

Thanks ! Cheers, John