Well, I haven't found the reason for loosing the dirt effect, doesn't appear to be the normals, those objects weren't touched and the normals are correct.
The issue with the fur shader on the Velcro was that I made a small section of the cockpit texture transparent and that broke the fur shader for some reason?
I suppose if it broke that effect it might have been the cause of the dirt effect being broken, but removing the transparency didn't correct the fur effect.
I'm still trying to sort this out.
This really seems like something got massively corrupted somewhere along the line.
Yes, it was caused by changing massive amounts of double sided mesh to single sided mesh. That had an adverse reaction of flipping some normals. Why, I guess you'd have to ask the folks that created Blender. I really don't see why it should have done that to some mesh yet not others. I see no difference in the ones that were changed VS ones that weren't. I feel it was worth it to me as I think I gained at least a few FPS after doing it. Then again. how much of that gain was from normals pointing the wrong way?
Maybe there is a way to prevent it but I don't know enough of Blender internals or options to know what that might be.
Anyway, I corrected the normals on panel R11U.
As far as the fur and possibly the dirt effect. I know what caused the fur shader to break (not why). Still looking for the cause of the dirt shader breaking.
I saw something els that I thought I corrected long ago. It's a minor issue but needs fixed just the same. The first image is after I already moved it some. That is better than what you may be seeing in your current versions.
Velcro is behind the cabin wall mesh.
Yet in the blend it is well away from the wall.
You can clearly see a gap.
There are no transformations as far as I can see for either the wall or the Velcro so I am at a loss to explain this?