What was found
IN FLIGHT HYD QTY SLOWLY DECREASING ABOUT 1 % EVERY 2-3 MINS TO 68 %. CREW STATED ACFT DEPARTED WITH 97 % ON A SYS HYDS & 102 ON B SYS. STATED AT 36,000 FT -A- SYS STARTED DROPPING A % EVERY FEW MINS UNTIL AT 68 %. RETURNED TO ORD. WHEN LANDING GEAR EXTENDED HYD SYSS LEVELS RETURNED TO NORMAL. ALL SYS OPS CHECKED OK. WHEN ACFT AT GATE NO SIGN OF HYD LEAK. A & B RES GUAGES IN WELLS SHOWED FULL. IN FLT DECK PANEL LEVELS READ 95% IN -A- SYS & 102 IN -B-. COULD NOT FULLY DUPLICATE FAULT AS DESCRIBED IN PIRED, VERIFIED NO LEAKS & NO MIGRATION FROM EITHER SYS. AS PERCAUTION R & R SYS A HYDC QTY TRANSMITTER IAW AMM 29-33-12-000-801. SYS REQUIRES SERVICING & OPS CHECK. PERFORMED HYD LEAK CHKS & AND GEAR SWING. SERVICED HYDS TO FULL & ACCOMPLISHED OPS CHECK ON TRANSMITTER. IAW AMM TASK 29-33-12-400-801. ALL CHECKS GOOD.