Define 'badly rusted' - if it hasn't actually broken, it will probably clean up OK. If it really is on the point of giving up, new springs are available - drop me a line with the engine type/code numbers.
If you remove the spring (carefully!), and examine it properly, you can make a decision to replace or not. It CAN be replaced by hand, but the feeder device you mention works.
phil_saunders@bigfoot.com
Phil Saunders, July 2008