How does the 6.25 in. PVC Base Vent Pipe Flashing with Adjustable Rubber Collar seal to the metal base on the roof ?

The Roof Collar does not seal to the base.

The Roof Collar does not seal to the base. Because of the larger size of these collars they cover the entire, existing, elastomer collar. It can be used to instantly repair a leak during a wet period, until the flashing can be replaced at a later time. The collars offer a better appearance than a mastic repair job.