I have a water chiller with 3 Copeland Discus compressors. The number 1 compressor was off so I reset oil pressure switch and added 3 lbs of R-22 refridgerant. On start up I saw bubbles in the oil sight glass. During these events the valve head became very hot. While checking the unit further I found a small pin hole leak in the copper tubing. I serviced the unit, including changing the oil. I then restarted the unit and it ran fine, with no bubbles in the oil. 3 days later I checked this unit and again observed bubbles in the oil and the value head is extremely hot and low on Freon. What do you think the problem may be? I think Freon may be leaking through the pistons and the value head may need to be rebuilt. Please tell me you thoughts. Thank you for your help.