If you have a chimney leaking water, it could be several factors.
– Bad/corroded flashing
– Sealant worn out
– Siding deteriorated
But if your chimney is 30” wide or more it could be that you need a cricket /saddle installed to prevent further damage.
A Cricket/Saddle is a ridge structure built on the roof side of the chimney designed to divert water away from chimney surface, preventing leaks and rot/deterioration.
If you have been wondering why your chimney keeps leaking when you have already discarded the other conclusions, this might be your answer.
And once done not only will your chimney not leak anymore but you would have brought it up to code.