Fogging problem

[Stardust]

I've been getting a problem with the rear element of the Samyang 135 and Sharpstar reducer fogging up with my Atik 1-6 camera.

Just wondering if anyone might know the cause and solution. It only does when the cooler is running so I think it's being caused by the camera. I've taken things apart, aired and dried but it's still doing it. It obviously hasn't done it in previous years but had this issue mostly this year. I don't have a desiccant tablet, it's an argon filled chamber.  Incidentally a friend has the same is just started with an Atik osc. 

If i take the camera off and clear the fog it usually stays clear but a bit annoying with a screwed  up system.

Any thoughts or suggestions welcomed

thanks for looking

David