crankshaft balancing

Good day I have a problem with a crankshaft pulley bolt which was replaced with the washer but keeps coming loose. I torqued the bolt to spec and added lock tight. The previous garage quoated on a new crankshaft which I thought is crazy as the car runs fine, Im guessing they had the similiar...

Would anyone know the balancing formula used on the 5.0 V10 crankshafts? The most common formula is 50% reciprocating and 100% rotating for the bob weights but I have not been able to find any information specific to this engine. I am replacing stock rods and pistons with aftermarket and have a...