TBMK the regulator is a totally analogue device, so I don't think it's resettable. But I have to say that, every morning when I press the boot button, I wonder whether it's going to open. So, if I don't manage to nail the problem down, the set of battery tails through the vent might become a sought after accessory.
Very interesting. If you hear a noise when the ignition is off, I suggest that you take the blower air intake off and see if the blower is running: this is what I intend to do if I can repeat my high drain problem. If it is running then I think the problem is that a semiconductor in the regulator is breaking down and a new regulator should fix it.
The problems you have with the blower switching off after a clicking noise suggests to me that you have a relay problem. I would have thought that this would be the auxiliary pump relay in the relay box behind the main fuse box (it also supplies 12V to the regulator control circuitry) - but I don't know whether this is anywhere near the glove box in a LH drive car.
As for a leakage current of 40 mA, say, after 8 days you would have used up only 7.7 Ah so it could cause absolutely no problems with a decent 100Ah battery. So you must also have an intermittent, drainage current in the hundreds of mA range.
One thing to consider for those of us in the Winter months in the Northern Hemisphere:
I've noticed that, in the winter months, my S320 is in a "battle" to recharge the battery.
In colder temperatures, a battery holds less charge. I make short trips to run errands (grocery store, library, bank, etc.) Lots of "power-consumers" on, too. The headlights, fogs, climate control, seat heater(s), rear window defroster, etc, etc.
This is my third winter with my S320. To better maintain the charge of my battery, I put it on a charger for 24 hours (Saturday afternoon to Sunday afternoon, for example) every 2 weeks or so:
Make sure always that you NOT have your ignition "on" or the key in the ignition. Disconnect BOTH battery connections to charge.
I back my car into my garage, open the trunk/boot to charge.
This always returns my battery to full capacity, or as full as possible.
Make sure your trunk/boot light in not "on" when the lid is closed. I've heard that some battery-drain problems are caused by this.
Our W-140s "must" consume some nominal power, if just for the alarm and trunk and door lock receivers to monitor changing input.
Longer daylight, warmer temperatures, less power consumers in use and more frequent and LONGER car trips make maintenance charging of my battery unnecessary in the warmer spring and summer months.
Mercedes does mention to check the condition of our battery's charge frequently thoughout the year, too.
These cars drive a lot of electronics, comfort/convenience features, etc.
Topping Up My Battery,
Salt Lake City, Utah USA (expected low temperature tonight, 9 F!)
1997 S320, 88,300 miles (with a two year old Duralast battery from AutoZone)