I wanted to test my A7r for light leak issues.  I put the lens cap on the body, set ISO to 100 and the shutter speed to 30s.  To make sure its not anything related to the support electronics I took one image with the camera in a dark cabinet in a dark room (no windows, no lights).  This is the image straight out of Lightroom:

 

In a dark closet, straight out of Lightroom

Next, I went outside into the bright midday California sun, pointed the camera lens mount to the sun and took the same 30s exposure:

 

Direct SunDirect Sun

There is a bit of a light leak but considering this was in full sunlight and for 30s.  Next, I opened the both the port covers on the left and pointed them towards the sun and again a 30s exposure:

 

Ports openPorts open

Its actually not as bad, probably because any light leak is more from the mount and since that was point away from the sun, its less.  Finally I mounted a Sony Zeiss 24-70 f/4 OSS with the lens cap on and pointed that at the sun, again 30s exposure:

 

Lens attachedLens attached

Again, nothing pronounced especially considering the ambient light level and exposure time.  Then just for visualization purposes I then pushed all the files in Lightroom (+5 stops exposure, +100 shadows, +100 blacks).  Here they are in the same order:

 

Closet PushedCloset Pushed Direct Sun PushedDirect Sun Pushed Ports open PushedPorts open Pushed Lens attached PushedLens attached Pushed

So yea, there is light leaking.  The most egregious leaking is with the lens cap on and in broad daylight but no one shoots like that.  One could argue an issue with long exposures and 10-stop ND filters where exposures can get into the several second range in broad daylight but in that case, a lens is attached and a lot of the issue mitigated.  So at least for my body, I see the light leak as a non-issue.