drive belt tensioner on 1990 Mercury Grand Marquis

Do these tensioners weaken with time, if not do the smaller serpentine belts stretch over time

All the engine accessories (power steering pump, alternator, air conditioning compressor ect are all driven off one fan belt that takes many turns and twists around each component and around idlers and tensioners. Check the fan belt for cracks or contamination. The belts don't stretch most likely the tensioner cannot adequately tension the belt.