Insects? Deficiency?

the markings on the lower leaves are reminiscent of spider mites. check on the underside of the leaves on the discoloured one and use a magnifying glass. If you see them. you need to nuke the plant with some heavy miticides. something with Pyrethrin works well on them. The other pick on the healthier leaves looks like some baby larva, maybe from a caterpillar? The weird goop on the leave might have been where the eggs where. If this is the case a product called BT, sometimes branded as caterpillar killer can help. its a bacteria control method and when they eat it they get sick and die. Good Luck!