How can I prevent water from flowing into my carport under the wall plate?
I would consiter putting in a temporary wall a foot back. Remove the existing wall Or at least the rotted  wood cut it off at the bottom and pour a new stem wall that is taller. With the best method being to dig a new footing and put some perf pipe in a sock at the edge of the footing for drainage (Basicly a French drain). With a new stem wall the water won't be able to rot out the sill plate, with drainage the wall should not weep.