sticky drivers door latch from outside, inside's okay, lube hasn't helped
 

I have a 2009 S, and the driver's door latch is a little tough to open from the outside sometimes. Pushing the door in helps. Mechanic has lubed it a couple of times with something they said penetrates and stays, but it's getting worse not better.

I've read that the inside latches can suffer this sort of problem if the Bowden cable stretches or is sticky, but the door opens fine from the inside.

What's this likely to be for a definitive fix? The latching mechanism? Handle? How hard are they to get to & replace?

Thanks