Clockwise yes, funny you should mention that. I'm switching over to Nikon gear from having used an OM-1 for years that I decided to retire and it was one of the first things I noticed when I first handled an FM2 a while ago - everything's backwards.
Good call on the prism. I was being lazy. After removing the screen I can confirm the shutter release is working, it releases the mirror, but something prevents the mirror from moving more than a few millimeters. It must be the depth of field preview lever although there is no visible indication of this. Furthermore looking at the camera from above with the prism off I noticed the body cap is indeed visibly warped, and it is drawn in towards the camera on the side of the depth of field button. Probably not a coincidence. The lever itself that you can see moving in the mirror box also may be a little bent as it drags a little on the front of the box - this is hard to describe, and it is not bent in the direction you'd think it should be if it's interfering with the mirror, but rather away from the mirror.
So, could be worse than I thought. Probably a simple enough fix once you get the cap off and figure out exactly where the hang up is, but there has clearly been damage of some kind. Strange that there is none visible, no drops at least, and no damage to the box.
I'm looking into getting a refund. Hopefully I get to keep the camera, it's in great shape notwithstanding the above. If I keep it I may need to send it off for repair. I'm traveling at the moment otherwise I would have access to the myriad tools and household objects I would ordinarily misuse in order to loose this cap and irrevocably damage something. I'll try to follow up if I manage to get it fixed, in case anyone's interested.
Man, what a beautiful camera. . .