I just did a few test on the light leak since I am on leave and at home , with the Sun blasting into my window , I place the A7 facing the window and did a number of test shots using the following 
1. Cheap RJ adapter with CV 40mm 1.4
2. FE 28-75 
3. FE 35
4. La-ea4 only
5. La-ea4 with Sal 50mm 1.4
All shots at 30s , ISO 25,600 for all except RJ at 3200 , you will see why lol
1) Cheap Rj with CV 50mm 1.4 - ISO 3,200
		
		
	
	
No need to go to iso 25,600 to know that the Cheap RJ adapter is CMI ...T_T , or is this the case for all third party adapters ? Dont have the voigtlander or kipon to test
2)FE 28-75 , ISO 25,600
If you want to be anal, there is very very very slight light at lower left corner , but I would negligible and could be due to high iso artifacts. I am happy to say that no light leak issues in real world shooting situation.
3) FE 35mm , iso 25,600
Same conclusion as FE 28-75mm
4) La-ea4 only , ISO 25,600
Looks the same as the earlier two to me , with maybe more artefacts at the edges ?
5) La-ea4 with 50mm 1.4 , ISO 25,600 
This obviously has more visible artefacts maybe due to more metal components, but still acceptable to me to conclude no real light leak issues. 
Overall , I think the light leaks matter seems occur only at extreme shooting .