Sometimes contaminants in the regassed car AC system blow out a new or existing front seal, particals from the old lines or not picked up by a filter.. or defected high or low pressure inline AC switches.. will cause pressure build up.. and the compressor will leak out the front.  It does not automatically mean a compressor needs to be replaced.

Usually people will try and fix this by regassing... again.. or  changing a compressor or giving up.. or trying for a warranty claim if its new. But the issue is normally far from the compressor.. in any of the 15 or so area's of AC service and proceedures.  The compressor is a majority leak point.. pressure /oil can escape from there rather then elsewhere FIRST.

This is a upgraded FRONT SEAL  known as a LIP SEAL.. for the front shaft of era's of GM compressors along with the clip and a fitting guide....shown below, includes the snap ring and fitting tool.

Service Tip your qualified repairer will know... Once filled with oil, place or hold the new A/C Compressor with the front seal facing down for 1-3 minutes. This will help coat the seal with oil - if this seal is not lubricated before installation, refrigerant may leak.