Joined: Nov 2016
The factory headliner doesn't have glue, except at the ends where the windshield and back glass help hold it in place. It's just stitched and stretched between metal bows. But I would be reluctant to use steam. The material (if original) is incredibly brittle and frail. I accidentally put my finger through mine a while back. It's about as strong as a paper towel, but more crunchy.
I don't have any good advice on how to clean, but I think I'd avoid steam, for fear of making it wrinkle up.
I smile a lot. It makes people wonder what I'm up to...