It can be rebuilt, but I don't think GM services the parts-- they only have a complete hydro-booster. You may do a search and find a re-builder that will sell the parts you need.
I suggest you disassemble one and see what you need.
BE CAREFUL-- THE SILVER COLOR LARGE TUBE IS A ACCUMULATOR AND HAS A VERY STRONG SPRING AND CAN KILL IF NOT CAREFUL.
Chevy 04.5 LLY, 2X, shell, XDR, MikeL Heavy duty up-grade, 6spd, TransGo, deep pan, de-badged, 65 Gallon replacement Aero tank, LBZ-mp, Kennedy pump, shimmed, Pre-fuel filter, tow mirrors, BU cam, gauges, GPS, Sirius, bags, custom grille, fender vents, HD trans cooler- Curt front hitch, footwell lights, load lights, Studs, head gaskets.