initial checks for a hot bearing or oiling issues i usually only go 5 to 10 minutes, for final clearance and alignments have to be done when driver and compressor is all up to operating temperatures for the oil and coolant
have you checked to see if your coalescor has a hole in it allowing the oil to carry over, also check to see if the return line is open that takes oil from the filter housing back to the compressor inlet
had a simialr experience repairing a clients machine that had failed, the lube line to the bearings inside frame was cracked and starved the crank for oil
replace cylinder check valve, also check lubrication holes in cylinder they might have a build up or partial blockage from metal,scale,foreign material that is restricting flow.
has your purge pressure gone up and amount of purge gas used gone down, if so could be an indication of packing leakage into and pressuring up the distance piece allowing gas to get into crankcase and contaminate oil in the case
blowdown to upstream of suction control valve thru a small port valve, if bypass left open the unit will equalize, can be set to reclose at set pressure for strartup
detonation is your first indication, shown on panel/ecu or you can even hear it at times, these spikes in cylinder pressure and over temp of cylinder cause the damage