Should I replace or repair my dead/dying garage door?
Lots of things can be wrong with your garage door or opener:


It could be something as simple as needing to replace the springs. If they are torsion springs, you're going to want to consult a professional, as they can store a deadly amount of tension. Consider it as dangerous as electric repairs.
Some garage door openers operate on battery. You might need to replace them.
Some garage door openers have adjustable settings. This is probably not the problem because you've noticed a degradation in performance and haven't indicated fiddling with the settings at all.
It could be a misaligned track, causing unnecessary work for the motor.
If all else fails, it's the motor. It's cheaper to replace it!