According to an email from United, "Our maintenance division has recently completed an audit of each fleet type and taken inventory of problems. Based on that we have established a program to check the cabins of each aircraft every 400 to 1,000 flight hours. We will be identifying and repairing seats, carpets, galley equipment, lights and audio and video equipment."

That works out to every 30-75 days for longhaul aircraft, which would explain why problems persist.