My home, a center chimney cape, circa 1740 has 3 fireplaces. One, in our living room sometimes almost floods out during (some rainstorms) - the other 2 are always dry. We have a blue stone cap on chimney and when our roof was redone 2yrs ago we emphasized our leaking problem to the roofer who made sure the chimney was well flashed. We do not have liners and we suspect that the interior mortar may be compromised. Any ideas on why 1 fireplace is affected would be appreciated !