How old are your bags? I had a P38 years ago, and bags were old when I got it. Similar thing. RHF corner would leak down. Once I replaced all four bags, I never had trouble with them again. My son just got into an 07 L322, and we went into it knowing that 14 year old air bags were on the short list of needs. Sure enough, three days in to owning it, on a road trip, we blew a front spring. Not even a slow leaker either. it just completely gave out.
Rule of thumb is like 10 years on a set of bags. Also, you'll want to address a leaky spring ASAP because it will eat the air pump if you don't. There's kits out there for rebuilding the pump. There's kits for rebuilding the valve block too. But those repairs for the do-it-yourselfer are a little more involved than a spring.
But to your original question, I would place money on the leak being the air bag. I promise... you can't see enough of the air bag when it's installed to know for sure it's not leaking. If it's leaking down overnight, when the EAS and the vehicle are turned off, it can only be the airbag, the line to it, or the valve in the valve block. And the bag is 99% likely.
