Welcome aboard. Saw you over on FB and was gonna recommend coming here, but you figured it out already
Can you unlock the rear glass from the button on the dash? There is a solenoid in there that pops the latch. when you push the button do you hear a pop of the solenoid?
If not you can try the key in there and turn it slowly but don't force (half of the ones i have owned the key never worked right)
It the answers are both no, then the easiest way I have found is to pull off the trim above the glass on the inside and use 10mm wrench to take off the upper hinges, then open the back like a truck tailgate with the glass attached. you can then pop the cover loose on the bottom and reach in there and manually release the latch. you will need 2 more people to hold the glass as when you release it will drop on the ground if no one is holding it up. one person wont be able to keep it from falling on the ground. I learned that lol.
I have an excellent grille, $60 and you pay shipping