Metal Flashing is the Worst

Don't take it from me, take it from this wooden sill. Covering exterior wood trim with metal flashing is a bad idea. As soon as the caulk/paint/metal are at all compromised, water gets into and stays in the wood. Plus installing the flashing almost always entails nailing it into the wood, creating penetrations, which increase the access water has to get deeper into the wood.  And you don't notice the damage since it's covered by metal. I recommend removing metal flashing and then repairing or replacing the wood as needed. All exterior wood needs to be maintained in terms of paint and caulk annually or every two years to prevent issues.