bushman wrote:

The lexan just fits
in from the top onto a 1/4" shelf. Silicone was used last and is leaking.

Yep, silicone is intended for use with fastners.

Do a search here and .cruising. Tons of info.
I used Dow Corning 795. Seems to work
Sikaflex has a blended product that has more stick than the DC product.

Bob