One of my bikes seems to get a stiff headset (behave yourselves) when left unridden for a few days. The last couple of times this happened, I squirted some GT85 into the headset area and re-tightened all the bolts. It's fine when ridden daily but as soon as I leave it for a few days, the handlebars develop a strong resistance to turning. The headset is the standard one that came with the bike and done about 7k miles. Is it on it's way out?