Radiator Leaking

[GroupIII]

I have a 2005 Murano. Since March of 2010 the radiator has been replaced 5 times due to split seams, primarily in the "bottom tank". The car has been under dealer service since I purchased it and (fortunately) the first replacement was under the Nissan Service Plus Extended warranty. The dealer has replaced the radiators since without cost, but now they are trying to find other (expensive to me) reasons it may be failing. They replaced the thermostat today (at my expense) because they said a Nissan factory engineer said it could be that or they may need to tear down the engine! There is no evidence that the pressure cap has released (so it doesn;t seem like a pressure problem.

Has anyone else experienced this problem and if so, was it ever resolved?

Tnanks