Where the plumbing vent pipe exits through the roof shingles, there is a metal plate with a rubber gasket (boot) that stops water leaking into the attic.
The flashing boot will generally deteriorate and start leaking water into the attic after about twelve years, that’s long before it’s time to re-roof.
The boot needs to be replaced. That used to mean calling a roofer and having them lift the shingles and remove the metal plate with the attached boot.
No longer, they make replacement rubber seals (boots) that slide down the pipe without removing anything, easily done in a few minutes without tools for anyone who does not mind getting up on their roof.