What was found
LEFT ENG OIL STRAINER LIGHT FLICKERED, THEN CAME ON CONTINUOUSLY AFTER TAKEOFF. THE LT ENG WAS BROUGHT BACK TO IDLE. OIL PRESS, TEMP, & QTY NORMAL. EMER WAS DECLARED & FLIGHT RETURNED WITHOUT FURTHER INCIDENT. LT ENG WAS SHUT DOWN ON TAXI IN. ACFT REMOVED FROM SERVICE. R & R OIL FILTER DIFFERENTIAL PRESS SWITCH IAW AMM 79-35-01, LEAK & OPERATIONALLY CHECKED GOOD.