To be honest. Repacking headsets is rare. Depending on the headset it CAN be done but is usually left for people who have problems with bearings (huckers) or REALLY muddy areas.
Sealed are bearings in a silverring sealed by a rubber wall (something like that, my description skills suck)
Main types. BEarings in a retaining clip, and sealed. Sealed are my choice but thats cause I like in mud central. With the clip version I used to take my headset apart, clean the race, regrease bearings and put it back together...I never trusted it to stay clean
