Where skylights actually fail
Older bubble-style skylights from the eighties and nineties leak far more often at the curb flashing than through the acrylic dome itself. The metal step flashing and counter flashing that seal the curb to the roofing degrade well before the plastic does, and the leak usually shows up as a stain on the drywall a foot or two from the frame rather than directly under the glass.
Newer flat-glass skylights fail differently, usually at a cracked or delaminated seal on the glazing unit itself, which shows fogging between the panes rather than an active drip. That failure calls for unit replacement, not a flashing repair.
Reflashing versus replacing
Where the skylight unit itself is sound, a full reflash with a new kit solves the problem: new step flashing up both sides, a saddle or cricket on the uphill face for anything over two feet wide, and new ice barrier tucked under the whole assembly. This is the more common repair on units under fifteen years old.
Where the unit is older, foggy, or the frame has started to rot, replacement with a modern deck-mount skylight is usually the better spend once the roof is already open around it. The old curb is removed, the deck is checked and repaired if needed, and the new unit is set and flashed as part of the same visit.
Timing it with a re-roof
If a full roof replacement is already planned, any skylight on the roof gets attention at the same time, because the flashing work is far easier with the field shingle stripped back than as a standalone repair years later. Homeowners are told upfront if a skylight looks like it will need work during a replacement estimate, so there are no surprises mid-job.
Sizing and placement on an older house
A lot of the older capes and colonials around Fall River were never built with a skylight, and adding one means cutting rafters and framing a proper header, which changes the load path on that section of roof. That framing work gets checked before any glazing goes in, since a skylight set into a poorly framed opening is a leak waiting to happen regardless of how good the flashing kit is.
Placement matters as much as the framing. A skylight set too close to a valley or a step in the roofline complicates the flashing significantly, and a better spot a few feet over often solves the problem before it starts.