Mag drive motors are so simple that it is really easy to look them over. There are the coil of wire molded in the epoxy or plastic, the impeller and it's parts. So if we understand how it works, it should not be hard to sort out what is wrong.
The cord, plug or outlet could be bad so that is always a place to check. Stick something metal down in the impeller well and plug the unit in. You should feel the metal item jump a bit as the current flows though the coil. If not, the coil could be bad but more likely the cord or outlet need repair.
It's pretty hard for a permanent magnet to go bad but while you have the metal item, make sure it sticks to the magnet on the impeller. Then do some looking at the impeller part as there are some things you can miss. Don't lay it down somewhere where it might pick up a bunch of metal filings. There are a pain to get off a magnet! The magnet and the blades should have some looseness to them. The mag part should rotate just a bit before hitting a stop and making the blades turn. This is due to the small torgue from mag drive. The magnet needs to get a small bit of momentum built before picking up the extra drag of the blades. It may not start turning if it is stuck solid in some way. If the stop is broken off, the magnet may turn but not move the blades. Pull the shaft out and really look it over good for bends or wear. One way to pick up some defects you might miss is by putting the shaft on a flat surface in a dark area. Roll the shaft while shining a light under from the far side and you may spot light leaking under in worn spots. But be aware that there are times when the impeller or shaft are worn in ways that you can't see. It is also possible to have wear on the well itself that makes it noisy if you have not been in the habit of cleaning it well. Check any little rubber bushings at the shaft ends for anything odd like cracks or missing.
But when you know there are only very few, very simple parts, you should be able to sort how which is defective.
Thorough frequent cleaning is on eway to make them last longer.