What was found
BOI- NR 2 HYD QTY SLOWLY WENT TO ZERO IN FLT NR 2 HYD ISO VALVE CAUTION LIGHT ILLUM, NR 2 HYD PUMP CAUTION LIGHT THEN CAME ON ALONG WITH RUD HYD CAUTION LIGHT. AFTER THE 3 CAUTION LIGHTS CAME ON, ELE PRESS LIGHT ILLUM. CHECK LIST WAS RAN AND ALTERNATE GEAR EXTENSION ACCOMPLISHED. A/C WAS STOPPED ON RUNWAY AND TOWED TO GATE. REMOVED AND REPLACED NR 2 PCU PRESS LINE AND NR 2 ENG DRIVEN HYD PUMP. REPLACED PTU, FLUSHED NR 2 HYD SYS. OPERATIONAL CHECK GOOD. AIRCRAFT RETURNED TO SERVICE.