What was found
AFT FL 370 PRESSURIZATION CABIN CLIMB & DESCEND INDICATOR CYCLES CONSTANTLY 500 FPM UP THEN 300 FPM DOWN. RIGHT DUCT PRESSURE INDICATION FLUCTUATE FROM EQUAL TO +5 PSI COMPARED TO LEFT DUCT. ACFT GROUNDED. FOUND PRSOV VALVE CLOSED BUT STICKY WHEN MANUALLY OPENED. REMOVED AND REPLACED PRSOV IAW AMM 36-00-00-860-807, AMM 36-11-04-000-801, AND AMM 36-1104400-801 FROM 3, A THRU G. REMOVED AND REPLACED BLEED AIR REGULATOR IAW AMM 36-1103, OPS CHECKED GOOD. ON NR 2 ENGINE PERFORMED SYSTEM TEST IAW AMM 21-31-00. GROUND VERIFICATION GOOD, NO FAULTS NOTED. RAN ENGINE PNEUMATIC SYSTEM LEAK AND OPS CHECKED GOOD.