[augiedoggie]

Try shortening front brake lever plunger on master cylinder. You should have 2-5 mm free play at plunger before it touches piston. If you have free play you likely have plugged return port in master cylinder. This can sometimes be corrected by reverse bleeding. Pump brake to move pistons out slightly and manually return pistons into caliper bore simultaneously. The returning fluid sometimes clears blockage. If not the master cylinder would likely need cleaning/rebuild. Not likely caliper is causing your trouble as you claim pistons are movable. No worries about one piston moving before the other. It's normal. Check back as needed if problems persist

 

[augiedoggie]

Bad idea to put any petroleum grease or oil on any brake parts. Only use specified brake fluid or brake specific assembly lube. Best to remove any grease by cleaning pistons and flushing system with denatured alcohol. Your pistons do not retract themselves much when brake lever is released. The pistons only relax very slightly when lever is released to allow pads to release grip on rotor. The pads are designed to run near zero clearances to rotor. If slight drag noise is felt when wheel is rotated on stand and brakes grab when applied your condition is normal. If wheel is difficult to rotate when brake is released try to determine if master cylinder is holding pressure on by loosening bleeder screw and observe your drag. If it relaxes drag it would seem your master cylinder is your problem.

 

[augiedoggie]

Brake hydraulic system cannot self generate pressure. If you have opened bleeder screw and found no hydraulic pressure you would likely have mechanical defect causing your drag. Hopefully you are not confusing normal slight drag and pad contact when rotating tire as drag. You can expect slight rubbing sound when bike is on stand when rotating wheel. If you feel resistance to rotation it would likely indicate a brake drag. If trouble persists I would think trouble is mechanical and not hydraulic. Bad wheel bearings or incorrect wheel spacer can cause dimensional problem with caliper versus rotor dimension. Improper dimension can also be caused by caliper slider pin backing out from its threaded bore or perhaps incorrect brake pads or defective pads having too thick a friction surface. Just a few ideas. Check back as needed for assistance