Yes, my firing pin has play to it also, up and down, no side to side. I have not had any miss fires yet that I reemmber, maybe one but I kept pulling the trigger till it fired. Maybe the firing pin has a small bend in it?
I have shot a couple hundred 38's through it and a hundred or so 357s through it with out issue. I have read on other boards of the firing pin breaking, but not much about misfires. For the last month or so I have also been dry firing with snap caps several times per week so that has been another several hundred trigger pulls.
To measure the hammer spring all you do is remove the one grip screw adn one side of the grip, once that one side of the grip is off you will see in the handle a spring on a guide rod. Just use a caliper if you have one or a ruller and guestimate the length.
Thanks.