As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
BOTH RADAR DISPLAYS SHOWING ERRONEOUS RETURNS AT 9-10 O`CLOCK POSITION. BOTH MANUAL AND AUTO. GROUNDED-YES. PERFORMED RADAR OPERATIONS TEST SAW DIFFERENT PATTERNS ON LEFT AND RT DU'S. NIS WX RT IN SEA. PRECAUTIONARY REPLACED WXCNTL PANEL, REF B737-900 AMM 34-43-39/401. ACCOMPLISHED INSTALL TEST. TEST OPERATIONS NORMAL. IN ADDITION PERFORMED SYS TEST, REF AMM 34-43-00/501. LEFT AND RT WX PATTEERN SHOW SAME. IN MAN OR AUTO.