What you say contains a kernal of truth.  I do happen to have a blood relative who was part of the United Airlines maintenance crew in San Francisco.  He confided in me that during the Continental Airlines merger with UAL, "You wouldn't believe how much they were running their engines into the ground."  He shook his head as he recalled how decrepit the Continental fleet was towards the end, and was also convinced some maintenance logs had to have been doctored to explain this condition.