Opening an electric motor
So I put some penetrating oil in as suggested by @EdBeal, and then proceeded to pry the crap out of it to get it open. Took a little work but it did happen.  

Unfortunately, the previous owner leaving it out all winter didn't do it much good, and the motor is beyond the amount of money and time I want to put into it.

Fortunately I was able to get a hold of another one that's in much better shape, so the pool is happy again!