Appears to be a "Captive" Reservoir ... some movement (Rotational) can be normal.

If No leaks, you're good

 

Yup!

If it can be rotated a little bit, it just means that the whole assembly has a little bit of play in the frame bracket. It shouldn't affect the functionality or seal in any way.

 

Did this ever get resolved? I think I misunderstood and thought your entire master cyl was loose on the mounting bracket.

On my mac and don't know how to capture a pic on this machine LOL but you can see the whole assy here
http://partsfinder.onlinemicrofiche....R%20W/%20PEDAL

The long rod off the brake pedal screws into a push rod #28 that's just to the left end (and off the picture). The push rod has a ball end IIRC and goes into a cup in the actual piston. This allows the master cyl to be not perfectly aligned with the rod coming off the brake lever. When loose, it will wiggle in there a little bit.

 

I think its the way it is. It works fine and doesn't leak. I noticed it when i was changing fluid.