5D MKIII - ho to check light leak issue?

folks, while in the store, how do I check whether MKIII has the light leak issue?

With the cap on put it in av and and half press the shutter and look at the shutter speed. Turn the light on the top LCD while it's metering or after and look at the value again and see if it's different or changed. Not sure if ISO matters but I did mine at 800. Make sure you cover the eye piece too.

Truthfully it's not an issue. People flip out about it for no reason. Doesn't affect anything. Did 3 weddings and some car shoots with it and did not affect 1 shot.

I don't shoot in complete darkness nor with my cap on

Look at the sixth digit of the serial number. If it's 1 or 2 then the light leak issue affects it.