During a visit some weeks ago to my local dealer I got talking to a service guy there who mentioned that there had been a few Z's in with water leaks behind the dash.
Not sure if this is what you are experiencing ?
Apparently the problem is the wiring loom (s) on newer models that enters from the engine bay has been changed or routed differently to what it is like on earlier models, and is causing leaks into the glove box/ fuse box area and behind the dash on some newer Z's :eusa-think:
Apparently it was also affecting newer 308's, but again not the earlier models. Probably because the Z and 308 must use the same wiring loom and route. :eusa-think:
If I recall the fix is to replace all the affected looms and fuse box, but more importantly the whole wiring loom has to be re-routed as per earlier models, "a pig of a job" was the term used by the service guy.
I cannot remember the exact details about this issue, but I did mention it on here in a thread some time back.
I'm also not sure if this is only affecting the very newest models, ie 2013, or if it is starting on later year models up to 2013, but from what I could gather out of the conversation is that they have seen a couple of 2013 models with this issue and slightly older models, he said it is a newly flagged problem that no early models have yet to experience, hence re-routing the loom back to it's original route as per early models.
This is not necessarily the same issue you have, but it may be worth looking into.