thanks for the ideas guys. Not sure what I am going to try but probably will first try Phil's idea with the 'v-track' on the bottom of a router plate.
For those that mentioned power washing, I have done that but the space is so tight that it doesn't stay open for long. I think by cutting about a 3/16" groove I can maintain the look on the rounded edges of the deck boards, get the drainage I need, and hopefully keep straight enough lines that it still looks good.
I'll most likely do a test cut in a spot where it's not too noticeable or where I could replace the boards if it really doesn't go well. We shall see . . . . .
Rick