the mouth of a mushroom is quite small and from the pic, i can see that the "slime" is not coming from the mouth, rather from the coral itself! i am very certain that it is melting. take it out to smell. if it smells atrocious, it is melting. and you should remove it because it MAY spread to ur other frags. since ur frags are kinda stressed from fragging now, u want to prevent all bacteria and other stuff from infecting it. take out that red mushroom asap if it is really melting.
as for saving it, very hard....i have no idea how. maybe someone might know.