Fixing object orientation/parent to allow proper animation

I purchased a model of a diesel locomotive and loaded it into my scene. I want to animate the windshield wipers but one of the wipers is just floating in space with an odd local and world orientation. (The artist apparently just left it hanging there. 😀) The wiper's origin is back at the rear of the locomotive, as is the origin of every other one of the model's components.

Tasks required:

1. Move the origin to the base of the wiper arm. (Complete)

2. Attach the wiper to the appropriate face on the locomotive body that corresponds to where the wiper would be in the real world. (Complete)

3. Align the local z-axis of the wiper with the normal of the body face so that the wiper can be rotated around that axis to make it behave like a real wiper. (Done so far by eyeballing it. Would snapping help in this case? How to?)

4. Parent the wiper to an empty so the empty acts as a controller. (Necessary? Desired?)

5. Figure out how to set up the world orientation and transforms so that when animated, the wiper rotates around its local z-axis and not the world z-axis. Currently, the wiper rotates into/out of the body no matter which axis I rotate around. (Confused)

Thanks! Please direct me to a better place to post if here isn't appropriate!