Rather than breaking the screw, the fibre nut may have failed. I just read a thread on that this AM. some one on here with faster connection can point it out to you... that is if you do not find it first. The arm can come apart and be grease / repaired and put back together. I wish we were a whole lot closer, I would like to meet you two! And have fun playing with the arm to get it fixed, but .... Some of the more experienced members can help you get it back working.
My thought, leave the arm off, get a long piece of 5/8th all thread and set the dish to the satellite you want, and lock it down. Then you can get the W5 set up you need -- have success -- then go back and get the arm repaired as you have time, with the joy of success behind you.
I had a saying (47) years ago, "Remember, you want to dig a hole, not just use a shovel!" That statement meant, get the back hoe out, if the ground was too rocky to hand dig.
SO, remember, you want W5, not just auto move the dish!
ENJOY. You can do it!
POP