As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DESCENDING THROUGH FL 190, THE FORWARD PORTION OF AIRCRAFT EXPERIENCED A MODERATE BURNING RUBBER ODOR. DISSAPATED QUICKLY. ALL ELECTRICAL AND AIR CONDITION SYSTEMS WERE NORMAL. THE AIRCRAFT WAS GROUNDED. ACCOMPLISHED MCM 05-96-70, TYPE 4. REPLACED THE LT PRSOV IAW AMM 21-31-01. REPLACED PILOT PRESSURE REGULATOR IAW AMM 21-31-11.