Proudly American
Read the diagram from the roof upward
The flashing has a base integrated with the roof covering. Its upper opening surrounds the pipe. A storm collar wraps the pipe above that opening. In the DuraPlus manual these appear as separate components. Your installed chimney may have different parts, so look up its series rather than using a photograph to choose a replacement.
Match the proposed work to the water path
A quote to replace the band at the pipe does not necessarily include lifting roofing material or replacing the flashing base. Conversely, a new roof flashing does not explain the condition of an old collar. Ask which connection the provider believes is letting water in and what supports that conclusion.
Read the exclusions before comparing totals
A useful description might distinguish the identified factory component, who supplies it, whether the roofing must be opened, and how the finished junction will be checked. Keep all inspection of the actual roof and pipe with the professional. Bring the model paperwork and interior observations to the conversation.