You have an odour. Can't mistake black for grey with a smell test.
The 5er we had suffered a partially dropped fresh water tank that made the underbelly swell down. The fresh water tank is made of a plastic that can swell, but the black and grey tanks are stiff.
First cut the underbelly low point and let any water out--collect some in a bucket for a better smell test. As said, black Gorilla Tape works to repair the cut.
I am thinking just a water leak won't make the underbelly swell down, but first drain it. Ours never went back up flat in shape after the tank dropping episode.
The soaking wet pink insulation is a write off, ignore it. Probably didn't do any good anyway.
