What was found
AFT ENTRY DOOR CAUTION LIGHT. RAN QRH PROCEDURE LIGHT EXTINGUIS HED. PRESSURE NORMAL. DEBRIEFED CAPTAIN. LIGHT FLICKERED ON ALTITUDE CHANGE AT CRUISE. INSPECTED DOOR SWITCH, DOOR AND ASSOCIATED AREA. NO ABNORMALITIES NOTED. SUSPECT DOOR SWITCH NEEDS ADJUSTMENT. REQUEST MEL 5203B. DISPATCH DESK: 31 TOMC AND DISPATCH APPROVED, OK TO DEFER PER MEL 5203B. VERIFIED DOOR FULLY CLOSED AND LOCKED. COMPLIED WITH MEL 5203B REQUIREMENTS. RIGHT AFT SERVICE DOOR, RE-POSITION PLUNGER SNAP RING. CLEANED AND LUBBED PLUNGER AND SPRING. ADJUSTMENT WITHIN LIMITS, INDICATION LIGHT FUNCTIONS PROPERLY REF FIM 52-10 TASK 801 AND AMM 52-71-11-820-801.