While working on part and hiding faces using the 'change transparency' option on single faces, one cannot know if there are hidden faces.

During the design process, you can hide multiple faces, and forget along the way that you hide one or more faces.

If it was a body, it would be very easy to find out the hidden bodies. (show hidden bodies, or ctrl+shift+tab) but when dealing with faces, there is no tool for displaying them, and not even selecting them. How can I select these faces?  Maybe toggle off the 'change transparency'? 

One solution might be to manually go through every body in the featuremanager design tree, making sure all the faces are visible. This method is time consuming, are requires prior familiarity with the model, which isn't allways the case.