It’s been a frequent occurrence for years at Denver International Airport: Out-of-order escalators and moving walkways gum up the flow of crowds. Broken fixtures in bathrooms greet arriving passengers. The once-gleaming airport has lost its luster, for some, even as there’s evidence of billions of dollars being spent in other ways. Twenty-six years after DIA opened, it’s fallen behind on maintaining its original buildings and the tens of thousands of pieces of equipment, vehicles, machinery and moving parts that keep the airport running. A recent city audit and documents reviewed by The Denver Post show that the airport, nearly eight years into an effort to establish a preventive maintenance program, is not devoting nearly the attention or resources to the most basic tasks of upkeep as it has to recent projects bringing major renovations and expansions. The audit, released last month, characterized DIA as stuck on a reactive footing when it comes to maintenance.