Tens years after the date of last manufacture of the vehicle by Federal
Law.  I've heard the name of the law before can't remember it off the top
of my head but, It seems that back in the 50s? some car companies would end
sale of parts almost immediately after stoping production forcing people to
buy a new car.  Also, because of emissions concerns it was neccessary to
keep parts available for many things for the mandated extended warrranty
period on the pollution controls.  Congress stepped in and mandated ten
years.

Dave K.