In general:
- Campy brifters are rebuildable.
- Shimano brifters are disposable.
- SRAM - I have no info.
That said, here are a couple links I've saved from past discussions on Shimano:
http://www.facebook.com/pages/Shiman...r/137062087082
http://www.bikeforums.net/showthread...-rebuild-guide