I have a 2004 VW Touran TDi Sport. Recently, the boot lock has starting acting strangely. The boot will, of it's own accord, unlock itself and/or if unlocked will release itself onto the secondary catch. The boot has come completely open whilst driving around once. I have changed the lock mechanism and my mechanic says the wiring is sound where passing from the car body into the tailgate (boot). He thinks it might be a problem related to the control unit (corrosion) as he had this problem with an Audi before.

Any ideas what the problems might be? It seems to be worse after it's rained.