I have a customer that has called me after a year and started to have some leaking along the brick wall and upper chimney flashing.
TRG. Some of that "invisible" plastic cement?
I'm with Mike on this one. We can't see what we can't see!
My recommendation would be to meet him at the property, thoroughly inspect and diagnose the problem and come up with a solution! ;)
Did you use caulking to seal the chase in the brickwork ?