Luck with that.......... ....heat warps and biodegrades the plastic and cannot get away from that. Usually not enough mounting points and I generally remount with additional mounts if it begins to crack. That pretty much stops it. Glue really unless a non-stressed part of grille will not work, it'll simply crack again just past the glue joint. Vibration figures in there a bunch. It adds up at the mounting points and in the long unsupported spots. If the plastic has biodegraded enough so you can cut off crumblies with a fingernail give up, the plastic is dead. Don't waste your time gluing up like a screw boss, putting the screw in will simply crack it again.

Mine cracked and a new previously non-existent mount put right there stopped it for years. You have to make sure it fits perfect, warp any and it simply breaks again. I spent like ten minutes shimming it just right to be a slip fit.

Epoxy, and not the quick dry ones, they are much weaker........ ......the 24 hr. stuff. If actual joint will be hidden then put metal of some type across the joint to bring the strength up 10X what the glue by itself will hold. Glue by itself is weak, but layer it thinly and other substance in there to add strength...... .............. ...well,............................they make airplane wings out of that.

Luck.......... ............an d Merry Christmas