Larry, the point of failure on these is almost always the grease inside the gearbox. You have two options, first heat the motor/gearbox assy with a heat gun and plug it in. Around 50% of the time this is enough to get it running again..
Option two is an alcohol soak. You'll start seeing grease seep out and when you do try to move it manually. If it frees up let it dry and drip in some 3 in 1 oil.