One of the major difficulties I faced when I began repairing Seiko Kinetic watches and replacing the Capacitors in them was removing the case backs.
Many Seiko Kinetics are over 20 years old.
The case backs are often stuck so firmly it is as if they are welded shut.
This is a brief description of one way I found works for me.
I hope that it is of assistance to you, also.
I glue a common lug nut onto the back of the watch.
I have shown 3 common types of Seiko Kinetic case backs in the photo.
Women's Seiko Kinetic case backs are exactly the same except slightly smaller.
As you know some Seiko Kinetics have a see-through case back.
This does not present an obstacle to this method of case back removal because the lug nuts I use are wider than the glass. The lug nuts touch the metal so when the lug nut is turned the metal turns, as well as the glass.
I use very small tubes of Krazy Glue because when I use the typical larger tubes I just end up wasting Krazy Glue. because the glue sets before I use that tube again.
I glue the lug nut to the case back, use a common wrench to turn the lug nut and loosen the case back.
Then I simply place the case back with the lug nut attached to it in Acetone, often sold as fingernail polish remover.
The Acetone dissolves the cyanoacrylate that is the Krazy Glue, leaving the lug nut and case back completely separated.
I have a 2 ounce coffee spoon I use frequently.
Or the top of a common medication bottle works well also. (See Photos)
When I have done the repairs on the watch, or I have installed the new Capacitor, I spray WD40 Contact Cleaner onto a Q-tip and run the Q-tip around the circumference of the case back.
I spray the glass window with Windex to get rid of fingerprints.
I then apply sealant around the case back.
Then I place the new gasket ("O-ring"), and screw the case back into place.
The sealant and the new gasket helps increase water resistance.
The WD40 Contact Cleaner makes the case back go back on more easily, and also ensures that the next time the case back needs to be removed it will be a much smoother process.