Actuator repair parts
Try Phil at the Parts Shop (top of the page links you there) - he may carry actuator repair parts.
If not - George Murphy carries actuator repair parts (865) 482-9175. I'm not sure if he carries a repair kit for this particular actuator, but I know he carries them for the HVAC actuators.
Personally, I'd just buy a new actuator - PartsShop should have it for less than $40 - and perhaps as low as $25.