Front drivers side door latch either won't latch or latch then won't open

What is your question?

The little white teflon lever sometimes comes up to latch the lock shut & other times it doesn't. I've tried coating it with Slick 50 and played with it trying to loosen things up but no help. What seems to make the problem better or worse? Everyday use How long have you had this problem? Started a few months ago, been getting worse, now doesn't work.