many times i have got another years' service from a headset by...
1.strip out and thoroughly clean.
2. inspect crown race/upper and lower cup for pits. if not too bad, re-grease.
3. inspect bearing races. if they readily fallout of cage then, bang some new races in, top and bottom.
4. more grease to the lot and re-fit, enjoy.
lastly, if pitting to crown race and cups is excessive then, get a new headset.
also, you may notice wear/pitting to surfaces are isloated to one third of the surface area( as this is the 'impact' zone. you can often remove cup and rotate quarter turn to fresher metal.
god luck.