My '86 F150 just decided to flush it's radiator in my driveway! The leak (gush) is coming from the drain petcock. Is it even possible for a petcock to cease functioning all-of-a-sudden like? Is it possible to replace a petcock or will I have to replace the whole radiator? And does anybody have any idea what a fair price would be for a radiator for a '86 F150?

Plastic tank?

If so, you can easily replace the petcock, most parts stores sell them under the "HELP" brand.

They are plastic, and when overtightened, they can break as they cool because the center plastic is not strong enough and as it cools it shrinks and snaps it in half.