I just bought a new home, and water is getting into one corner of the house. The drywall on the inside of the pictured corner is soft and there was mold under the baseboard, but no water marks are visible from the inside. The bad drywall only extends about 6 inches up from the floor. Our realtor said the previous owners poured a new step at the front entrance, and thought it was likely that the step was trapping water against the trim, and water was wicking up into the interior of the wall.
Question 1: What should I check to find out if this really is the source of the water?
This is the outside wall: The affected drywall is inside the corner with the gutter and along the wall by the step. I see no evidence that the gutter or downspout are leaking.
When it rains, water pools in the slot by the step.
A closer view: As you can see, the trim extends several inches below the step. The siding is LP (circa 1990, so not good stuff), but the trim is wood. The trim appears undamaged.
Question 2: If this is the source of the water, how can stop water from infiltrating into the house?
One suggestion I've gotten is to cut the trim above the step and install metal flashing. I'm not sure what I should expect to find behind the trim, nor where/how to attach the flashing. The house foundation probably extends some distance up behind the trim, but I would also expect there to be some form of vapor barrier back there which I would rather not damage. What can be done to enable proper drainage of the slot next to the step?
Location is the Seattle area, so lots of low intensity rain and dampness. The house was built in 1990, and it is in good shape but the build quality isn't the highest.