there is no danger with lemishine cleaning cases. Its actually how the ARSENALS clean cases. It actually helps preserve the cases.
Though there is no real reason to let it soak for more then 5-10 minutes if the water is hot.
A lot of signs of bad cases are not reliable at all. Like case separation,, the old trick of bent paper clip down inside the case to check the case for separation near the primer FAILS 30% of factory new brass from Winchester in .308