As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
TROUBLESHOOT LOW HYDRAULIC LEVEL DURING GEAR RETRACTION, UPON INSPECTION IT WAS FOUND THAT THE HYDRAULIC SYSTEM VENTED THE RESERVOIR OUT THE DRAIN MAST NEAR THE NOSE LANDING GEAR. PERFORMED GEAR SWINGS AND FUNCTIONAL CHECKS PER C-550B M.M. 32-01-00 WITH NO DEFECTS NOTED. SUSPECT A FAILING HYDRAULIC DUMP VALVE TO BE THE CAUSE OF THE ISSUE. CUSTOMER AGREED TO CHANGE THE VALVE