Concur with all the above - no silicone here and I really like the Permatex Right Stuff - it's got some type of rubber-like compound in it that seems to be pliable, fills little microscopic imperfections, and impervious to the heat generated in the water pump application. I use a little bead on all sides and assemble right away as this - stuff starts to set right away.

(I used a lot of Gasgacinch when building dirt bikes (two-strokes) and it seemed to work well for cases and water passages - also really easy to take apart. But you're not wanting to take your pump apart on a regular basis!!)