I have a 2012 SEL with a power liftgate. On Saturday, I noticed it was creaking a bit when I opened it. Yesterday it went about half way and stopped, if I push the button again it will finish going up. Today, it goes about 2 inches at a time. It seems to be the actual power power actuator not the hydraulics. Is there anything that I can do to lubricate that or does it have to be replaced?