What was found
CLIMBING THRU FL 410 AMBER "HYD VOLUME LOW B" EICAS MSG DISPLAYED. B-SIDE VOLUME SHOWED 18 PERCENT, DECREASED TO 16 PERCENT. RAN CHECKLIST. UNLOADED B PUMP. FLUID VISIBLE ON BELLY BETWEEN MAIN GEAR WELLS. GAIN ACCESS. REMOVED AFT FUSELAGE BELLY PANELS CLEANED. RAN RT ENGINE PRESSURIZED SYSTEM FOUND B SYSTEM PRESSURE FILTER BOWL LEAKING REMOVED PRESSURE FILTER HYD. HOUSING ASSY. REMOVED AND REPLACED O-RING. LEAK CHECKED SATISFACTORY IAW MM 29-10-08.