My home was built in 1902. This season, I installed a new gas furnace in the basement, (82%+), to replace an oil-fired furnace. I went into the attic recently and noticed that a dark brown/black tarry smelly liquid is leaching and bubbling through the bricks and mortar at about the last six feet of the chimney before it exits at the roof peak. The attic, (3rd floor), is non-heated. As is the case with older chimneys, the chimney angles away from vertical at the attic floor until it reaches the peak. The bottom and adjacent sides of the chimney are where the liquid is leaching. Do I have a condensate problem since installing the gas furnace? Does it appear a liner is in order? Thank you for any help!