Most times when a corner leaks down it's because the corner valve leaks the air back to the reservoir. Thats what I'm basing that statement on. I know I've had to get involved in a handful of cars like this. It usually ends up being the reservoir leaking, or the line that runs over the top of the reservoir. Crap from the road will build up between the frame and the reservoir and makes it rust thru. You should have a spray bottle with a little dish soap and lots of water. Get that bottom half of the cover out of your way and spray the shit out of anything that looks like it could leak air.