Put the motor back (you dont even have to screw it on) and take two paper clips. One paper clip goes to the black wire and the other to the orange wire. Dont let the paperclips touch eachother; you will burn the fuse and be without radio. Then touch the wires to the two terminals on the motor. If it goes in the wrong direction just wire it the other way. Then try to close the trunk. If it's too far down the trunk wont close. Shove something in the hole where the motor was afterwards, otherwise your trunk will gradually open as you drive. You can also take out those screws like you said and manually adjust it, but by hotwiring the motor you are eliminating that as the problem, or proving that it is the problem.
90% of the time, from my experience, the paddle switch on top of the motor is what starts acting up. On mine I drilled out the rivets , cleaned the contacts inside and then bought some screws at ACE to replace the rivets. On my dads it was the connection between the paddle switch and the motor. I took a file and cleaned the contact surfaces and then bent them to give a stronger contact.