I had it apart last week. I cleaned it up inside, and reassembled it. I checked it to ensure it was functioning properly. I can take is apart again, though.
I'm not sure I understand how this starter works, but it's always engaged with the drive gear. The gear reduction unit is inside the side cover of the engine, on the right side. There's a clutch inside that will only turn one way. At first I thought that maybe something had fallen apart inside the cover when I removed the starter, but there's nothing to fall apart. The only other thing I can think of is that for some reason the starter clutch stopped working. The clutch is behind the generator, and doesn't look like it's too easy to get to. With only 14.6 hours on it, I wouldn't think the starter clutch went bad suddenly.
Could it somehow be operating in reverse of the correct way it's supposed to turn?