[mikefocke]

Coming in on top of the clamshell? Air comes over the top and then swirls toward the front. Presses the water forward.

So what comes to mind:

Have you gummifleg'ed the old seals or otherwise tried a product to make them more flexible?
Are you sure the spinlocks are as far down as they need to be?
Have you screwed down the top as much as you can?

Drain locations are under the clamshell, one on each side.