Why is water leaking on the vent pipe?

Hello! Our vent pipe in the basement shows water running down the surface after heavy rain. Usually the day after, and not during.

We’ve asked 2 roofers to come and check the roof and attic, and it doesn’t seem there’s any issue with the roof.

I’ve asked a plumber to use a pipe camera, and it detected no cracks. If the crack is too small, the camera won’t pick it up.

Now the next step is to break the walls, and check the pipes that way. Does anyone have any suggestions on what we could try before breaking the walls?

Thank you!