Don't know whether you've taken it fully apart, but if you have, you might use a magnifier to see if there are any significant scratches or burrs on the washers/bushings in the pivot. If so, burnishing or sanding/polishing the washers or bushings might make the biggest difference, especially since the lubes you've tried haven't helped yet (suggests the source of the friction is too big/coarse for the lube/oil to compensate).