Here's the TWU study on outsourcing:
http://www.twu562.org/2011/03-11/Aircraft%20Maintenance%20-Maintained%20in%20America%20Final%20March%203-2011.pdf
And of course, some maintenance issues arise that are unrelated to outsourcing, like this one:
http://www.tulsaworld.com/business/article.aspx?subjectid=45&articleid=20110407_45_E1_Arepor109652
http://www.twu562.org/2011/03-11/Aircraft%20Maintenance%20-Maintained%20in%20America%20Final%20March%203-2011.pdf
And of course, some maintenance issues arise that are unrelated to outsourcing, like this one:
Five 737-300s were removed from service by Southwest after fuselage cracks were found during inspections. Southwest executives said the five planes will be out of service until a repair plan is drafted with Boeing Co.
Although Aeroman in El Salvador has performed about 15 percent of Southwest's heavy maintenance since 2009, the last heavy maintenance overhaul of the damaged 737-300 was carried out at the company's Dallas maintenance base, Flaningan said.
http://www.tulsaworld.com/business/article.aspx?subjectid=45&articleid=20110407_45_E1_Arepor109652