I have a simple cinder block garage. It is exposed on one side and adjacent to a neighbor's garage (6" gap) on the other. The side adjacent to my neighbor shows some water spots on the inside of the wall, which become more prominent when it rains. I have attached several photos below, taken after a couple days of rain (although the spots never really clear, they just become more prominent after rain).
The garage is about 5 years old. For the first 4 years (before I owned it) my neighbor's garage did not have a gutter and therefore poured water onto that wall everytime it rained. When I first saw water spots inside my garage, about a year ago, I attributed it to the missing gutter. I spoke with my neighbor, and at my request he kindly installed a gutter April 2016.
The problem is that a year later I still see what appear to be water spots inside my garage. I would have assumed it was just efflorescence / staining, but the spots seem to be more prominent when it rains.
I checked the outside wall, and it actually seems drier than inside - so I think my neighbor's gutter is working fine. I considered that maybe my roof is leaking and pouring water into the wall, but I don't think so. The roof line hangs over the wall, so I am pretty sure I would see dripping into my garage in order for it to get in the wall (the roof line is perfectly dry, as far as I can tell).
There is a bit of pooling on the flat root, but very minor and the wet spots traverse the whole wall (not just the back corner where there is a little water on the roof).
The opposite wall, which is exposed, is completely dry inside and out.
Is anyone please able to explain what might be going on? What can I do to resolve this?