I think I found the root of my evil...I took off the calipar again and slipped out my pads, then pumped the brakes. This pushed out the piston and there is a boot from the egde of the piston going into the calipar. That is ripped/torn which I guess is supposed to hold in some grease or other lubricant, allowing the piston to freely retract after the brake pedal is released. I'm guessing that lubricant has probably leaked out thus slowing the retraction of the piston. I'm guessing my solution will be to get a new calipar. Again, it's just the driver's side front that is causing the vibration and the wheel (rim, rotor and calipar) gets fairly hot under light to normal braking. Thepassenger frontside is cool to the touch (or at least a normal temperature that you'd expect).

 

That's just a dust boot. There's a rubber piston-ring that seals the fluid, but that boot just keeps the piston & cylinder bore clean. But like you say, if it gets dirty it might not push back in like it should.

You can get those rubber peices (#1 caliper seal kit)& rebuild the caliper, but that's a pain & sometimes a rebuilt caliper is pretty reasonable.