Had the same thing on a 53, blame the French. Japanese car, BUT the book lock made by Renault. Have a look on Ebay for something called K12 boot repair. (I think.) Basically water is getting into the mechanism. For 99p the guy on ebay sends you an email with pictures and instructions on how to fix. As long as you can handle a screwdriver, and bend into the corners it's pretty simple repair.
Antony
December 2011