Reasons for failure of Hp element in ZR-250 Compressor (0-15 bar)

we are using 6 no's Atlas copco ZR-250 (0-15 Bar range) screw compressors in that recently one of the compressor while starting and compressor in unloading condition(approximately 15 minutes, because there is no air requirement). Observed that noise & smoking with sparks coming through the enclosure at outlet air line surroundings and stops the machine immediately. After opened & inspecting the service person and found that Hp element screws are not rotating and he said element is damaged due to mal-function of IC drain valves, moisture is carryover in to the element. My observations: Running Hrs:19968 Loading Hrs:13064 Load/Unload times:1,49,000 Slight Bearing Clearance observed in drive bearing(which the shaft pinion gear is placed) as compared to other bearing. Is it possible to carryover the moisture during unloading condition? and i am not agree with his reason. so please give your probable reasons for failure of HP Element & also give the allowable clearances for Hp element Bearings. And also give suggestions for smooth operation.