What was found
AFTER TAKEOFF FROM MSP ON FLIGHT 3156, CONFIG WARNING, TCAS, OAT HEAT FAILURE. AIR RETURN TO MSP. MAINTENANCE FOUND LT MLG STRUT BELOW SERVICE LIMITS FOR NITROGEN, HYD. FLUID, EXTENSION CURVE, ALSO NOTED FLUID LEAKING FROM STRUT. REMOVED AND REPLACED SHOCK STRUT SEAL ON LT MLG IAW TASK CARD 3211-301. OPS CHECK AND LEAK CHECK GOOD.