Today could have been a VERY expensive day. Fortunately my wife is Awesome (with a capital A), and noticed before anything bad happened. But let me back up a little bit.
A couple weeks ago, I noticed the typical crack forming in the coolant expansion tank.

So, one FCP euro order later, I had a gallon of coolant concentrate, new tank, and cap.
Out with the old:

In with the new:
.
Notice the large hose under the tank. It has they usual german spring clip. Well....I vacuumed the system, waited to see if there was any reduction in vacuum for several minutes, then filled the system. Started the car, checked for leaks, drove it around, topped off, and all good, right?
A couple days later, I drove to work and noticed the coolant was low. OK, must have burped a bit. Got home and topped off. Drove it again a few days later and burped again. No biggie, topped off and called it good. Today, my wife drove the car to work. About halfway into her drive, she called me. "I see white smoke coming out from behind the car. I'm pulling over. Oh E36 M3, the low coolant light just came on. I'm pulled over and shut the car off".
berkeley!!!!!!!!
I leave work and get to her 45 minutes later. "Temp gauge never climbed," she told me, "the light was on for less than 500ft". I pop the bonnet. Tank is almost empty, but everything seems to be in place. I pull on the large hose under the tank and it pops out. That berkeleying spring clip wasn't seated right. I start to look up road side assistance. However, there is a reputable Euro shop (BIG shout out to Steve's European Auto!) two miles away. I give them a call. "Hey, I'm just down the street from you. Any chance you can bring some coolant out to us so I can drive the car to your shop?" 15 min later a porter comes out with a coolant jug and a funnel. I reset the hose and we fill the coolant. Start the car up, no visible leaks and head out to their shop. As we pull in, they have a bright red with gold wheels Lamborghini Countach parked out front, a Rolls, and a newer V12 Ferrari among the Audis, Porsches, etc. I get out and pop the bonnet again, still hear a hissing. I wiggle the hose and it makes a squishing noise from the joint and there is coolant dripping from under the car. Damn. So I leave the it with them, drop my wife off at home and get back to work just in time for my meeting. This is about 9:30a.m. when I leave the shop.
I call them on the way to work as I was thinking through what I did and how this may have happened. I asked them to replace the hose for piece of mind and that when I was working on the tank, that clip may have pulled out more than it should have to remove the hose and maybe didn't seat properly. I get a call around 1:00 p.m. They got the car in and did find the spring clip not seated properly, so they fixed that. They pressure tested the system (I only have a vacuum fill tool, now I need to buy a pressure tester), and it held pressure. Topped everything off, drove up to temperature, checked for leaks and then called me. They said hose doesn't need to be replaced, it was in great condition, but we will if you want to. I was OK with keeping it if they were comfortable. So for the road side rescue and the fast service, the total bill was $150!
Huge thanks again to Steve's European Auto of Waterford, MI for saving my butt.
Phew!