So initially the dealer didn’t know it had bulk heads and is toons are compartmentalized? If so, that would be worrisome. Should be common knowledge on the Benningtons.
Honestly, given what you describe, it doesn’t seem like a weight distribution issue. So that would only really leave a leak and water getting into those pontoons. I can appreciate why everyone is stumped given the lack of significant water being drained out of them.
Since they got some water out, clearly there is a leak of some sort. So after draining, and testing, they can verify NO water left in the pontoons? Is there any chance that the way they are draining it isn’t getting at most of the water? For repairs, are they sending it to a skilled aluminum welder or just “giving it a go“ in house? I’m puzzled too given what you have shared.
As for the source of the leak, do some searches in the forums. There are some of us that have had a leak issue over the years, had them repaired, and haven’t had problems since.
There seems to be a coupe common causes. Our leak issue in 2020 was related to the welds along our port side performance foils. I think the most common source is weld points. For us, our port tubes were drilled, drained and plugs put in. Then they redid the wields along the entire performance foil and no problems since. The leaks were incredibly tiny pin-prick type leaks along the wield points. You would not have seen them at all if not for water draining out through them because the tube would fill up significantly past that point…so it would drain down to those wields when I put it up on its Sea Legs.
I think a couple others had some water getting in from the top of their tubes along the “M” brackets in an older model/configuration. In the end, if they cannot fix/prevent the leaks from happening, then draining and plugging is not solving that issue. For the life of me, I don’t know what else would cause such a noticeable list…