As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
RETURNED TO DEPARTURE DUE TO STRONG BURNING RUBBER ODOR AROUND EMERGENCY EXIT ROWS. ACFT WAS AT FL330, ODOR DISSIPATED ON DESCENT AND WAS GONE BY TOUCHDOWN. PERFORMED OPERATION 5088 (SIC TROUBLESHOOTING) ITEM 3 FOUND LIGHT BALLAST B6-53 BAD. R & R SAME. RAN ENGINES AND COULD NOT DUPLICATE.