Door actuator problem

My front driver-side door has some intermittent issue...sometimes it locks, and sometimes it doesn't after hitting the LOCK button on the remote.
I have a 2011 GLK...w/ 24k miles.
Should be under warranty, right?
Pete
Corrosion on the contacts is the usual culprit; the good news is it's easy to clean with light sandpaper or Scotchbrite...


