AutoCAD 2013 :: Rotated Sections Through Extrusion

Acad 2013 on a capable Windows 7 machine.

I would like to cut a section through an extrusion. Attached find a section view of my extrusion cut at 90%%d. My deal is I want to be able to specify the angle. It could be anything, and it could be a compound miter (using in saw-speak, because my drawings go to saw operators), that is, angles in two directions. But, let's keep it simple - how to cut a section parallel with the Y axis in the attached drawing? 

Right now I am warping something in due to the complexity of the profile. But for accuracy sake it is obvious why I'd like something better. I'd like my operators to have confidence in what they see. 

I could do this easily in Inventor. Or even oin Civil 3D, working around it (using Autodesk-speak). But, I have neither. Is this a UCS thing? I trained myself to never touch the UCS long ago, because I am a surveyor by trade, and surveyors pull coordinates from AutoCAD (or one of its children) to stake points on the ground with, and a surveyor ends up working at McD's if she/he goes outside with coords pulled from a made-up UCS. So I don't know the first thing about manipulating the UCS, despite daily use of the products since release 12.

I looked at Sections in the 3D modeling workspace palettes, but nothing really jumped out at me for being able to rotate or cut sections where I want them to be. They all seem to snap to existing planes of the extruded solid. Big deal - I can do that intuitively just by looking at the part.