Stack?

What is a cracked stack?

A cracked stack at the roof wouldn't cause leaks inside the house. A compromised stack flashing at the roof easily could. A cast iron stack would take a lot to crack it, but pvc, not as much. It would bend some prior to cracking, though. Hard to tell without being there, though. How old are the boys? Got a digital camera...send them up and take lots of pics - at least one should help tell what's going on. They'll get a kick out of it.

Have them crawl up in the attic. If you can see light around the stack as it goes through the roof, then rain can and will run down the outside of the stack potentially all the way into the basement. If you have a telephoto lense, take on of the stack as it comes through the roof from outside, then, blow it up in your computer. You might be able to see something. DO you have a pair of binoculars or a small telescope - check it out.

stack..

It won't take long to give it a test.

Two problems solved by just talking to a friend who knows.

I bet he is very happy to be of help to you.

Have you heard of doing this with the roof and a bonnet? If so, how common of a procedure is it, if you don't mind me asking these questions. Also, does it work well?

stack

Sure, I see them all the time on motor home vents and chimneys on homes.
Keeps most water out and squirrels out .

Keep it just far enough above to allow the vent pipe to function.

The diagnosis now is water that falls into the roof vent finds its way to the outside of the pipe through a crack or hole.

That hole may be touching wood or insulation and capillary action draws it out and it eventually collects in places below.