My dad had this problem with a Cavalier, the rear light seals had perished. I only mention this as the c-max lights are so high up on the c pillar.
04 plate Ink Blue 1.8 Duratec Ghia. Mods so far, club sticker on rear window and stereo upgrade, 4Q sticker on bootlid and Smurf hanging from rear bumper.
More mods to come as i\'m allowed to.