front brakes- pads, rotors, and calipers

Just a guess here. Since your master cylinder brake fluid level "never" lowered I I think you should open the master cylinder (remove its cap) and either drain the old fluid completely (especially if real old and dirty) OR just go through the same bleed routine onthe front wheels again with the master cylinder's cap removed so that any air in the line up there can escape through the master cylinder into the atmosphere. If you have no brake line leaks at all (at the wheels or master cylinder) then it has to be a bad master cylinder itself, one of the calipers, or defective bleed screw(s). IMHO Hope this helps.

Then there is air trapped in that antilock rabs unit, some of these have a bleeder screw that helps when bleeding the system, if yours has a bleeder screw make sure you bleed the system with the key turned on. Others need a scanner to activate the system during bleeding.

G A's answer is quite interesting to me. I will also be learning from this. Please let us all know (this forum) what fixed this so that we also can benefit from this information sharing. Teachable Wayne here. Thanks.