Realize this is a 2 yr old post, but felt an update was needed.
Discovered Castrol LMA (Low Moisture Absorption) Brake Fluid lots of years ago. With my limo company, standard practice is a brake fluid flush every 2 years using Castrol LMA. In addition to the LMA properties, it also has a higher boiling point.
As far as master cylinder rebuilds, NAPA generally inventories the rubber pucks. A quick brake hone of the cylinder bore & replacement of the rubber & spring(s), followed by a bench bleed & refitting and your master cylinder is ready to give you trouble-free service for many more miles.