The plastic a/c vent vanes that let you direct the air left/right (driver/passenger) have gotten to the point where they a sometimes very difficult to move using the "tab." Is this a silicone spray fix? Other suggestions? Thanks!
Have you tried removing the vent panels to take a closer look at them? If I remember correctly, the vents are hinged/levered, so maybe there's crud blocking them from moving around. Or a hinge is loose/broken and isn't in its original position, such that you need to push it back into place. FWIW, removing the dashboard panels should be a fairly simple job that doesn't require much technical know-how.