Assuming you've got wheel cylinders and/or a master cylinder that's not pitted, rebuilding is OK. We did it for many years, before ambulance-chasing lawyers got into the act. Most professional shops just won't take the liability risk of rebuilding brake parts, because the parts manufacturers have got deeper pockets in case of a lawsuit. If new parts are available, I'd rather use them, especially on the old single-line brake systems where even one failed part results in a total loss of brakes. When the choice is between rebuliding a part that's 50+ years old, or using a new one, I'll err on the side of caution every time.
Jerry
