A B737'S HYD SYSTEMS WERE SERVICED AFTER THE CREW FOUND LOW A HYD SYS QTY. A MECH SAID NO LEAK; BUT HYD FLUID WAS FOUND FLOWING UNDER THE RIGHT WING AT THE NEXT DEST.

Narrative

I WAS SETTING UP THE COCKPIT AS THE CAPT DID THE WALKAROUND. I NOTICED THE HYD LEVEL SYS A AT 81%. I NOTIFIED THE CAPT WHEN HE RETURNED AND HE CALLED FOR MAINT TO HAVE THE HYD SYS SVCED. HE ALSO ASKED ME TO DO AN OUTSIDE CHK FOR ANY SIGNS OF HYD LEAKS. AS I WAS IN THE WHEEL WELL ON THE #2 GEAR SIDE; CONTRACT MAINT ARRIVED. I SAW NO INDICATION OF A LEAK IN THE WHEEL WELL AND MOVED OUT OF THE WAY SO MAINT COULD DO HIS JOB. AS I STEPPED BACK I NOTICED A WET SPOT ON THE PAVEMENT APPROX 2 SQ FT BESIDE THE #2 MAINS. I FELT THE FLUID AND IT WAS SLIPPERY; LIKE OIL OR HYD FLUID. I ASKED THE MECH WHAT TYPE OF FLUID IT WAS AND IF IT CAME FROM OUR PLANE. HE TOLD ME IT WAS NOT FROM OUR PLANE. AS HE WAS VISUALLY INSPECTING THE HYD SYS AT THE TIME; I FIGURED HE COULD TELL IF THERE WAS A LEAK FROM OUR ACFT; AFTER ALL; HE IS A MECH. I WENT BACK TO THE CAPT AND RPTED THAT THE MECH WAS SVCING OUR HYD AND WHAT HE HAD TOLD ME. WE DEPARTED WITH FULL HYD FLUID IN BOTH SYS BUT UPON LNDG IN ZZZ SYS A WAS AT 92%. A MECH MET US AT THE GATE IN ZZZ1 AND SAID HE OBSERVED HYD FLUID DRIPPING FROM THE R WING. IT WAS IN FACT A LEAK IN THE A HYD SYS. SUPPLEMENTAL INFO FROM ACN 804964: UPON ARRIVING ZZZ1 AT THE GATE; FLUID WAS COMING ALL OUT OVER THE R WING ROOT AREA NOTICED BY A MECH AND SAID IT PROBABLY WAS A LEAK WITH A PUDDLE ON THE GND AT GATE. A HYD NOW SHOWED 92% AFTER ENG SHUTDOWN AND WAS 100% IN ZZZ. HE PROCEEDED TO TELL ME THAT AT SOME STATIONS HE KNOWS ABOUT ARE SENDING RAMP AGENTS WHO DO WALKAROUNDS OUT TO WIPE DOWN AIRPLANES BEFORE THE CREWS ARRIVE TO AVOID DELAYS. THE MECH KNEW THAT IT AT LEAST HAPPENED IN ZZZ2 AND I'M HOPING THAT IT DIDN'T HAPPEN TO US IN ZZZ1 BUT DON'T KNOW. 1) I DON'T WANT ANYBODY TO INCLUDE RAMP OR PLTS DOING WIPE-DOWNS OF ANY FLUID WITHOUT A PROPER WRITE-UP TO MAINT. 2) IF THIS IS A STATION DIRECTED POLICY THEN IT SHOULD BE STOPPED.