I recently moved into a flat, some parts of the bathroom floot tiles the grout is slowly cracking and loosing and crumbling away, usually where its moist, its discoloured yellowish, its not caused by water left on it as someparts near the bath are fine , its mainly under then toilet i know there is a small leak,
also i have these earwig type insects that come out at night -
The earwig insects love damp conditions - cure the damp and then get rid of them.
Where exactly is your toilet leaking ? If it is from the flexible joint between the bowl and the waste pipe if there is a rubber seal replace it.
If it is from the seal at the back where the pipe from the cistern connects - replace it.
If it is from the cistern itself - turn of the water unscrew the siphon and reseal it.