Speccing out springs is such a pain. I've never really been successful, even using the Machinist Handbook for the math tables.
What I do now is go to Ace Hardware. The good ones have assortments of hundreds of different springs. Then I try to pick a close one.
Or you could just get new arms...
Your wiper spring inside the arm is worn out, and the arm is not pushing down hard enough. OR there is some crap in the hinge area keeping it slightly propped up.