Other sources of leaks:

1. Trunk lid star - 13mm bolt to remove star and inspect.
2. Trunk lid emblems - holes on each side holding down the emblems. Tiny grommets holding emblems in place may have fallen off.
3. Antenna mast seal - there are two, outer and inner.
4. Quarter panel moulding fasteners - if they go bad they can allow moisture inside. There is a maybe 8 or 10mm bolt at the corner of the quarter panel holding this trim piece to the car.
5. Tail light seals and seals under tail light
6. Fuel filler neck seal - allows water into trunk if not sealing properly.
7. Trunk lid "stops" on either side/rear corner of trunk lid

If water gets in and pools, when ambient temps go up the water collects on the inner surface of trunk lid.