I'll add a word of caution, it is not uncommon for a caliper to not seal when re-assembled after being dis-assembled.
This has been attributed to metal warp, from years of braking/heating cycles.
If at all possible, do the piston seal replacement without splitting the caliper.
You may get lucky and have no leaks, but if the caliper does not seal, you will probably have to replace it.(hence why dealers shy away from doing caliper rebuilds)