My microwave vents to the roof and leaks during heavy rain. How do I fix it

We have a sloped roof and the vent is close to a valley. We went up and installed taller flashing and roofing tar to seal under the new flashing and thought we had diverted the water that comes down the valley. Apparently not! I do have the manufacturer of my modular looking into it. But since they were the ones who last worked on it I am sceptical of their abilities and this is why I am trying to get more info.
Maybe I need to get a qualified roofer out for a look.

A picture may help us better understand. Is it the vent or the flashing around the vent?

Flat or slope roof? 99% of leaks at vents are either poor caulking, loos nails securing the boot or a crack in the boot around the vent pipe.. Need to go up and look.

Taller flashing because the water washes over the evnt? Most flashing fails right at the roof shingle connection not up top. Tell us more or post a pic. Any good roofer would be done with this in 15 minutes but most DIYers can do it too. It should not have been installed near a valley.

My microwave vents to the side of the house an it lets water in during rain storms. What would cause that and how do I fix it? Would it be possible to fix it from the inside? Thanks for any help. Georgia Myatt