Where you are adjusting the balance, just to the right, there are 2 bushings with grease nipples, grease them lots. Put some blocks under cutter bar just to the inside of where it flexes, see if the weight of header can get it to move, if so get it moving and grease more. Those bushings will seize up.
We actually just dealt with one like that today. Worked fine when we put it away, was greased, but still seized on us.