A common practice of many roofers is to replace some but not all your existing flashings. Re-used roof flashings are prone to leakage and detract from the finished appearance of the new roof.
A quality, metal flashing should be installed at all the critical areas of your roof:
Step (sidewall )
(especially if you have a brick chimney)
(be sure these are solid lead with a lead cap)
When available use 26 gauge, enamel coated metal flashing. Metal last longer than rubberized flashings and provides a beautiful, finished look to your new roof!