Here is an old style Glasser frog where there was a big crack in the front part of the frog. These old style frogs do not have an underslide, so simply glueing the crack most likely will not hold up. This is an expermental repair, that should hold up for years and only took a few minutes of repair time. Here are the steps.
Glue the Crack
Trim a piece of fiber that's a little bigger than the frog and drill a center hole.
Wet the fiber and clamp overnight so that it is molded to the correct shape.
The next photo shows how it is now formed to the correct shape.
Glue the molded fiber to the bottom of the frog, so that it's now the underlside.