Don't know much about the 190, but isn't there a coolant pump that is supposed to circulate the coolant after engine shut down. If the 190 has one of those, I'd check there, perhaps a hose is brittle and releases minute or even more coolant at a crack.
Again, not sure if the 190 has that pump!

Nope, not on the 190e. There's an auxillary pump but it only runs with the heater on to keep the heat working at idle as far as I know.

You can get UV dye that you can put into your coolant to trace a leak.

I used the Bar's stop leak before without incident and I like to keep it circulating in my system to keep everything lubed. Yes, it stays in the system forever and I had to flush my engine like 3 times to get it all out. Anyways, I was able to identify the leak. It was the bypass hose going from the water pump to the cylinder block! @#$*ing Mercedes! That hose is maybe 2-3 inches long and the gap between the clynder block and water pump is maybe is thick as 2 nickels! The entire water pump, sterrping pump, belt, and maybe belt tensioner must be removed to get to it. I bought a grinder the other day because I planned on grinding down a little bit of the cylinder block side, but the grinder would not fit. I then started sawing at it with a small hacksaw, but I was not able to make much progress. After analyzing the situation a bit more because I refuse to take everything apart to replace a small hose, especially since that may cause me to open up a can of worms in regards to my belt tensioner and water pump, I decided to cut 1/4 inch of the rubber hose I had then I lightly greased the edges of bothe sides. I was able to put it in between the small opening at a 90* angle and slowly work it around the cylinder block side. Then I slid it back as far as it would go towards the cylinder block and I pushed the remaining part down and then pulled it forward to cover the water pump side. Hose replaced. Take that, MB engineers! Problem has been solved.

be careful of bars,I found it only effective in american cars and trucks.It seems japanese and german cars,have smaller core row sizes.It seems everytime I have used it,my radiator turns into concrete.I use aluma seal in stead.Its really fine power,passes thru are rows easy,and seals leaks.I use it every anti freeze cleansing,as a precaution

Heil mein Fuhrer,
damn Mercedes engineers, you showed them!!!!

Great, you fixed it and it hopefully will hold up.

Yep, sometimes they engineer in such way that the stuff has to be put together in a sequence.
On the other hand, as these things get more and more complex, it is hard to engineer something that is also easy to repair, besides, a Mercedes never breaks anyway, yeah right!

Thanks for the tip. I've seen stuff like that with the aluminum particles. I actually ran something like that in my engine a while back. It was a headgasket block seal type of thing. I did it as a preventative action just in case. Engine is at 351,000 miles. Despite its few repairs here and there, its still going strong. One thing I am proud to say is that I opened up my valve cover and looked at the cooling system insides and everything is extremely clean. No gunk on my valve cover, and not one trace of rust in the cooling system