If it were me, I'd contact Audio Technica customer service, explain your issue, and see what they recommend. Maybe they have an idea we haven't come up with here; maybe there's an authorized service center near you; maybe they'll suggest sending it to them for a look; since you think it's the headshell, maybe they'll agree that's a reasonable guess and send you a new one [Edit: maybe they'll think SterlingOne's guess is even better]. I wouldn't pay a local service to play with it or do anything myself that might void the warranty.