What was found
AFTER GEAR RETRACTION, RIGHT MAIN GEAR RED UNSAFE LIGHT REMAINED ILLUMINATED. CYCLED GEAR AND LIGHT EXTINGUISHED, THEN ILLUMINATED AGAIN. AIRCRAFT RETURNED TO MDW AND MADE AN UNEVENTFUL LANDING. REPLACED GEAR PROXIMITY SENSOR, RIGHT GEAR UPLOCK SWITCH AND SEALS AT PRIORITY VALVE PER BOEING M/M.