I have the frame apart on my '85 Hobie - mostly to re-rivet the x-bars, to shim the pylons and to install the new tramp. My foam plugs looked kind of deteriorated and I decided to remove them. On my Hobie they seemed like they were siliconed in place - but not very securely. I found water (a few ounces) in each pylon. No loose lead in my pylons. The hulls were drained many weeks ago when the boat was used the last time. It seems like the opening in the pylon that allows the hulls to ventilate is drilled higher than the "shoe" that holds the bottom of the pylon so that water cannot drain back into the hull.
I would like to replace the pylon plugs - it looks like they are made from closed cell polyethylene (looks like Ethafoam) - IIRC other sailor used swimming aids (like aqua noodles) to plug the pylons.
Any other ideas that might work???