To work on the exhaust, I have removed the rear bumper cover and bumper. Yesterday I noticed a sort of crack in the glue kind of stuff on the chassis, see picture below. On the left side of the car (where this picture is taken) it runs quite a way forward. Also around the rear part. On the right side It is only visible around the bumper post, not running forward along the main chassis beam.
I have taken quite a bit of the car apart over the last year, with a lot of carpeting, panels, heat shields and liners removed and I have not seen this in other places.
A few questions on this;
1. What is this glue kind of stuff called?
2. What would be the cause of these cracks?
3. Are they structural or only cosmetic?
4. Any advice on a fix?
Marc_986 
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