Ben and carl,

I guess I wasn't too clear. the leak is where the multiport valve mates with the sand filter body. There is a 2 part plastic clamp which holds the two together. As mentioned, when I fired the system up, it was leaking where the two clamp halves meet (at the bolts). I took it apart, cleaned the mating surfaces, lubed and installed a new O-ring. I even thought the clamp was binding a bit on the flange, so I put some lithium grease on the inside "V" surface of the clamp, and in fact it did close tighter than before, and it didn't leak at all. But about 2-3 hours later, it was leaking. I'll try the sand next.

not sure what else to try after that?

thanks