Some good(ish) advice from Cyclic Hotline there, however I'd argue "The MD 500 is the worst helicopter ever built." and strongly argue "6. Do not try to reason this in a scientific method, or you will go completely insane - try random solutions."
I had my first attempt at balancing a 500 this year (having previously balanced two and three bladed aircraft) and the process was trickier, but by no means an unscientific one. The process of tracking, correction and consequence can be followed, though it can be a lot harder with a multi bladed head (as I found out!). It is absolutely true though that, if it all starts to go wrong, the easiest thing to do is is to start from scratch.
Hopefully nouseforaname has pm'd the name of the 500 man I'm thinking of to fling-wing_1!