The answer to 'why is my fascia leaking' is that the fascia board, which is the horizontal board that runs along the edge of the roof, has likely developed a crack, hole, or other damage that is allowing water to seep through. This can be caused by weathering, rot, or improper installation. Symptoms may include water stains, peeling paint, or visible damage to the fascia itself.
To fix a leaking fascia, you'll need to first identify and address the root cause of the issue. This may involve replacing damaged sections of the fascia, sealing cracks or holes, or even replacing the entire fascia board if the damage is extensive. In some cases, the issue may be related to other roofing components, such as gutters or flashing, that will also need to be repaired.