Hi again I have seen damp spotting similar to this, but only on a chimney breast caused by water entering chimey stack at high level and seeping down through loose fill and coming out through the breast. It is possible that you could have the same happen in a rubble stone wall but unlikey in a cavity wall. I think it unlikely that leaking gutters would cause the problem that you have because the damp seems just too high.(this is just my opinion)
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