Den,I hope you can get the caliper piston to release using the master cylinder/brake fluid.
I think you should have a close look at your fork tubes,in the 'areas of travel' i.e. the parts of fork tubes that make contact inside the fork 'lowers'.
You can inspect the upper parts which are in contact with the fork seals to see if there's rust or pitting from flying rocks,etc. which shoots off the back of vehicle's tires and hits that part of the fork 'travel area' which can make your seals tear and leak later on.
I wouldn't sand down a fork tube,especially in the 'travel areas' and the part of the tubes which are down inside the lowers;sanding down a fork tube will reduce it's O.D. and cause a loose fit inside the lowers which will will cause the front-end to wobble
When you find nicks in the seals area,you can get a small piece of like #400 sandpaper and then only use your fingernail to soften Just the sharp edges around the small nicks to keep from cutting your new fork seal's.
I recommend using a micrometer or calipers and measure the O.D. of the full 'travel areas' of each fork tube to see if the O.D. is not below the minimum O.D. according to your shop manual specs.
I hope your fork tubes 'pass muster' in those wear-areas of measurement,otherwise it's best to replace the tubes with a fresh pair.
Depending on the amount of mileage(wear between them)and how often the fork oil was changed... also take a dry-fit of both the 'lowers' and fork tubes to see if there's any 'wiggle'/movement between them. The 'lowers' being aluminum wear also.
