Owners of 2008-09 Chevy Cobalts, HHRs and Malibus, along with Pontiac G5, G6 and Solstice models (all with 2.0-, 2.2- and 2.4-liter engines) may complain of an engine oil leak that seems to emanate from just under the air conditioning compressor.
One likely cause of the oil leak is engine block porosity at the rear A/C compressor mounting bracket bolt hole. The good news is that the bolt hole isn't under pressure, so the leak can be sealed off rather easily.
To do the job, remove the rear bolt from the A/C compressor mounting bracket. Now clean both the bolt and bolt hole with brake cleaner, then dry with compressed air.
To complete the fix, apply either Teflon pipe thread sealant or Locktite 565 sealant to the mounting bracket bolt threads, reinstall the bolt and torque to specification.