Wiper motor keeps failing

There are a couple things that can cause this. First and foremost is a sub-par product that you are replacing the motor with. Unfortunately there are quiet a few motors out there that are not good quality and they will fail pretty quickly.

The other cause could be the other components that are connected to the motor such as the arms are binding or loose which causes the motor to work too hard and it wears out.

Take a look at the info attached on replacement and make sure these mounting bolts and the arm joints are not loose or binding. If they are not, try switching to a different brand of motor.

You are definitely correct. The arm keeps loosening up and I tighten it but it still continues until the motor eventually goes out. What can I do to keep it from getting loose?

If I am not mistaken, you should have the arms that go onto a splined stud and then a nut that tightens them down? If that is the case, then you can put some removable/blue thread locker on the threads and that should keep the nuts from backing off.

However, if these splines on that stud are getting rounded off then you may have to replace both the arm assembly and the actual wiper arms as well.

Get some pictures of where it is loose and we can give a better idea if this doesn't seem to match what you are seeing.