Our Philadelphia rowhouse side alley door sill (door itself is a Stanley steel door) over a stone threshold has been failing for some time (moisture, of course) to the point where the piece of wood that the metal sill was attached to is gone. Husband has temporarily shimmed and duct-taped the sill in place. Do we fill the gap below the sill (open to the basement foundation wall) with cement and then try to flash it? Someone said to remove the metal sill threshold (already done, currently duct-taped and shimmed in place), fill the voids with hydraulic cement or pressure treated lumber and sealant, add a flashing pan or flashing set in sealant, then replace or install a new metal sill/threshold with sealant again.  Sounds good; any other concerns/suggestions?