New rebuild kit, DOT 4 fluid, s.s. lines if you don't already have 'em, & consider disassembling the calipers for a good cleaning of the pistons' outside circumference, long as they are apart, replace the square o-rings for the pistons too. After nearly 15 years you'd like a good cleaning too! If you want to cheap-out, you can replace the piston in the master, but you should clean the caliper pistons as they accumulate material after 14+ years which can affect the way they retract. Dremel w/a brass brush or a flapper wheel, scotchbrite pad, or 120/180 grit wet-or-dry sandpaper. Clean everything twice, reassemble & don't forget some lubrication for the caliper piston o-ring, you can use fluid where they touch ea. other. I blow-out the lines & splitter w/compressed air & see what kind of volume is through them, brake lines can partially or completely collapse internally, but of course you would have noticed that because usually your pistons in the calipers won't retract if it's a complete blockage.
