As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AT C-CHECK MAINTENANCE, UAL DISCOVERED 20 INCHES OF OUTBOARD END OF FILLER WAS MISSING FROM THE NR 1 SLAT SEAL. THIS FILLER WAS INSTALLED PER THE MANUFACTURER. SUPPLEMENTAL DATA UPDATE UAL SUSPECTS THAT TENSION WAS INDUCED DURING THE INSTALLATION OF THE BULB SEAL FILLER, CAUSING IT TO EVENTUALLY TEAR AND BREAK. EVENTUALLY IT WORKED ITS WAY OUT OF THE BULB SEAL DURING SERVICE.