First time post to this forum, so hello all!

At one of our sites we have a 400 ton RTHC, water cooled that has had a history of running oil loss problems. We have checked oil sensor, charge, master oil solenoid, oil filter(s), etc.,. I don't have it with me but every item in the IOM manual for running oil has been checked. The chiller will run for a week, a month, 2 months and then go down.
This last Sunday we had another shut down on oil. When I arrived, I checked the oil sump level, 7". Trane says 2-6" is good. I set up my VOM on the optical oil sensor and started the machine. It started up fine, with a .24VDC optical oil signal. It ran about 10 minutes. I then heard a click and a slight clunk from the pueblo loop (oil filter area), the optical oil signal immediately went to 19.89VDC(never saw that happen), and the machine shut down in 5 seconds on running oil loss. When I looked thru the optical oil sensor site glass, the line appeared empty.
Per Trane Service Bulletin:
0-2VDC = wet reading (all oil optically sensed)
2-20VDC = foam optically sensed
>10VDC = after delay, will shut down chiller on running oil loss
*these values are from memory, correct me if needed

I thought it was the master oil solenoid dropping out. I got another pair of eyes on the job. we set up min/max VOM's across the pressure switch and starter contacts that could drop out the k400 contactor that would close the master oil solenoid, drain the pueblo loop, and dump the machine. We ran the machine and the problem never reoccurred. The chiller has been running since.
Has anyone had oil problems like this on an RHTC?
Is there any do's and don'ts any one can pass along on this type of machine?
Yes, I am planning on going to an RTHC class this winter. But we gotta get thru this problem first.

CHW Setpoint = 42*
Tower Water Setpoint = 78* Low Speed, 82* Hi Speed
Discharge Superheat = 18-26*

Cond Approach = 2* - I know, a little low. But we recently found another chiller connected to the loop that has a evap to chw refrigerant leak. The chw had a lot of foam in it(glycol protected) and I don't think the evap on the RTHC was loaded as good as it is now. Previously, at setpoint, we ran 22-28% loaded and now that we've isoloted the other chiller and bled the system, we are running 38-44% loaded at setpoint. Anyway, my next visit I'll add some 134a.

Evap Approach = 6* - Another variable as the other chiller is tee'd into the RTHC chiler's supply with a B&G Flow Setter in between each to cause a pressure drop to feed the other chiller. Real down and dirty and another brilliant engineering cost cutter. Bottom line, I'll have to check flow thru the RTHC to verify where it's at right now.

Suction = 33#
Discharge = 103#

Any help on this issue would be greatly appreciated. Our backs are to the wall as the other chiller down for evap repairs right now is our backup to this chiller. Without it, a good part of the campus is without chilled water.
TIA for all replies,