I have a home built in 1930. It has a chimney running thru the center of the house 1 1/2 stories thru the roof to the basement where the furnace is. On the second floor the chimney is leaking thru the plaster which is around the ceiling and it is causing bubbles to form thru the paint and a little mold going on. I had the chimney repaired 2 years ago with new flashing because it was also leaking in the same areas. This time due to a huge amount of rain in April it started leaking again. What could be the problem now and how can it me fixed?