My rear hatch lock failed during a cold snap a couple of weeks back. (thankfully in the unlocked position) I didn't want to hassle with taking it to the dealer under warranty, so this is what I found.
1. Traced vacuum leak to the hing area of the pass. side hatch.
2. Separated the rubber gasket that goes between hatch and body.
3. Found that they use a yellow PLASTIC hose, and it cracked in half. (very poor design)
4. I used a piece of rubber vacuum line to reconnect the two halves. (due to lack of extra line and other wires I used a pair of needle nose pliers to hold the plastic line while I slid the vacuum hose on.)
5. Reattached rubber gasket.

Total time, about 10 min.

This is most likely what the dealer would anyway, as I cannot see them replacing the whole line, and this will last ! If they did replace the whole line, it would probably break next winter anyway.

Hope this helps.