I have a 1987 RS...the rear hatch lock is "jammed" I can put the key in, but when i turn it, it feels like its jammed. It gets gradually harder to turn, then it doesnt go any more. It opened a week ago, I have no idea whats wrong. We tried lock lubricant, turning the key REALLY hard, and pushing the hatch itself up and down, nothing works. Are the locks easy to replace?