I'll be danged. I was wrong about seam sealer also. Theres probably sealer under the hinge or something. Been probably nearly ten years since I fixed a rear crash on one, so shoot me. I'm fading, thats one reason why I don't post much. Had enough snap to go look again though!
Here. I think this will get you closer.
Firmly bump the other end of that 2x4 with a sledge hammer (don't swing it just thump it, sneak up on the correct amount). Less than a 3 lb hammer prolly won't move it but maybe a pry bar or wrench? Hitting it will help it move down, bending with tool won't. Its a funky shaped striker but theres really no adjustment built in so you gotta bump it. I remember now. The rubber overslam bumper is lightly spring-loaded, just push that down.
Hope this helps
