I would use smooth-on epoxy to fix that separation. You can warm the two parts a little before mixing-- this will make it somewhat thinner, so you can work it into the separation better. Get some into the separation, then use thin unwaxed dental floss to work the epoxy all the way down into where the separation starts. Once you get the entire separation wetted with epoxy, clamp it together with spring clamps or other type of clamp. Wipe off excess and squeeze-out epoxy. You could put an incandescent work lamp on it to warm the epoxy and speed & strengthen the cure.
If the separation was an inch or less, I might use Loctite 420 superglue (or Hot Stuff CA superglue-- the least viscous [thinnest] version). This stuff is thin enough to wick all the way into the separation.