Leaking Metal Chimney Stack

[I'll have a go]

Hello, had a new roof installed four months ago. Since then, water has been dripping down the chimney stack around the seam area (image 1). We've had another roofer take a look at the chimney from the outside and he says the original installer has fitted it incorrectly/wrong way round? From the images, please could anybody explain why the water is getting inside the roof and what is possibly wrong with the installation. I didn't understand roofer 2's explanation. Many thanks for any advice in advance.

 

[cross thread]

If the two flues in the photos are in use for a gas fire get them tested ,the new one looks like a lash up to fit the old terminal,the old one fails all clearances .

 

[I'll have a go]

Hi, neither gas fire is in use as far as I know, certainly not ours although they are both potentially useable. Wasn't happy about the neighbours flue proximity but we had the new roof. We could possibly offer to pay to get his raised if he agreed. My immediate worry is the leak down the seam area. The original roofer has tried sealant but that's not worked. Somehow it,s getting in through a small gap somewhere between the metal casing and the rubber collar/sleeve?