Rear Brake lockup

Might not help but maybe it will? Those Packing seals came with different Kawasaki part numbers because of the change within but are identical, 43049-002 and 43049-1098. Make sure you clean off all the residue left in the caliper seal land, i use a curved dental pick but anything that gets underneath the shadowed area will work. Note there is a cut-out relief central to the seal bore, that's where a sharp but blunt tool comes in handy to get the old crap out. Check your "chrome plated" piston for pitting!! If it's flaking chrome/pitted where the packing seal resides, like one shown,      in bore it's going to forever leak. I always use assembly red rubber grease when doing mine but you might not have any?? Also check that rubber brake line for good measure. I've seen plenty of them internally plug-up with crap preventing fluid from flowing properly.   

i changed piston seal today. no leaking probleö. it is lock up . if any other idea i can try

Can you tell which pad is holding? Try and carefully ease the piston side pad away from the disc slightly- does it release ?

the piston side pad is stucking.  no it not release. unscrew bleed nipple no moving. just moving when unscrew the under caliper brake line screw. and i tried master clinder brake line connection screw  unscrew it is not mowing.

Put a ruler across the rotor.
Your rotor may be dished/warped.
Old style non-floating rotors dislike the uneven heating between the center of the rotor and outside of the rotor.
This may turn the rotor into a bowl.