As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ENROUTE, CREW RECEIVED "C HYD QTY" EICAS C MESSAGE, WITH PRESSURE C SYS NORMAL DURING CRUISE. INSTRUCTED TO RETURN TO DEPARTURE. AN EMERGENCY DECLARED. LANDED WITHOUT FURTHER INCIDENT. R & R HYD RESERVOIR FILL INDICATOR. UNIT FAILED INCOMING TEST. METER POINTER STICKING & FRICTION HIGH IN METER. WINDOW GLASS LEAKING, OVERHAULED UNIT. REPLACED WINDOW & BEZEL. REPLACED METER ASSEMBLY & RECALIBRATED THE UNIT. UNIT PASSED FINAL TEST.