What was found
(CAN) AFTER TAKE-OFF LEFT MAIN GEAR FAILED TO RETRACT. EICAS MSG `GEAR DISAGREE` AND `GEAR DOORS` WITH ASSOCIATED ANNUNCIATION LIGHTS. QRH PROCEDURE FOLLOWED WITH A NORMAL GEAR EXTENSION AND RETURNED TO LAND. UPON TROUBLESHOOTING FOUND THE LMLG SIDE STRUT ACTUATOR HAD FAILED INTERNALLY AT THE THREADED ATTACH POINT OF THE ACTUATOR. THE SIDE STRUT ACTUATOR WAS REPLACED AND AIRCRAFT RETURNED TO SERVICE. (TC# 20190628013)