I'm about 1/2 finished with the first splash guard.
There was a longitudinal crack at the top of the arch. and a couple cracks at the front, where the bolt is, and near where the headlamp wire goes through.
I first tacked the crack together using GOOP, and then used a cut-up antifreeze jug to form a patch, or backing piece. The patch was heated to the softening point with a heat gun, then placed over the crack, and formed to shape with a dry rag. The patch was then glued on the back of the part so it will not be seen. The patch was oversized to provide strength to the old, thinly-made splash guard.
I will do the same with the crack at the front; you just have to move quickly to get the backing piece to form well to to the splash guard.
Since the clips for the fender arch lip are not available, I will probably use a clip for electronics, such as below.