Originally Posted by Bill

So I pulled 30mmHg of vacuum from the AC system, but that only lasted 15 minutes. Checked lines - looked ok. Thanks to Super Werty for pointing me to the O-ring on the AC reservoir/dryer. When I installed the low pressure sensor, I left the OEM O-ring in place.
When I checked it, it was deformed (the sensor was not overtightened). I replaced the OEM O-ring with the green O-ring supplied by CSF (it was on the bolt originally installed on the reservoir/dryer). The low pressure sensor tightened perfectly and without deformation of the O-ring. My AC system is now holding 30mmHg of vacuum for the last several hours. The system will be recharged within the next few days, hopefully without any leaks.