One of the A&P's I work with said he thought the black poo goo was there to prevent oil canning and that it should not be removed. When I confessed that reconstituting and reinstalling the mess just wasn't going to happen, he said he thought glued on Selkirk type insulation panels should be fine to accomplish the same goal.
For what that's worth.

I had thought about the structural possibilities, but then, the why only the cabin? i'm still betting it was for an extra layer of sound insulation.

Chris

What exactly is "oil canning?"

soyAnarchisto wrote:What exactly is "oil canning?"

When the aircraft skin is slightly stretched between frames and/or ribs the skin will pop in and out like the bottom of an old school oil can.

It doesn't take long to find at least some slight oil canning on any Cessna. The goo was to help get rid of some of the "popping" sounds.