A local mechanic quoted me $300 to replace the leaking mono valve in my 87' 420SEL. Not wanting to put up the cash I pulled apart the valve with some help from you guys (thanks). Inside I found some calcium deposits. I scraped it clean with the tip of the the same flathead screwdriver I used to pull out the valve. Now the monovalve doesn't leak anymore and I can justify spending $300 on somthing a bit more fun!

I hope sombody gets some use out of this post

How do you know it's calcium and how in the world does calcium get inside there? ? Thanks.

My guess is that white subtance is alum. oxide real good idea to change coolant every year or so and to use coolant for alum MB engines.where is mono valve on 126......
William Rogers.......

You guys might be right. I never thought it was alm. oxide. I thought it was calcium from hard tap water that may have been in the systm. (like the stuff that collects on a showerhead) I didn't put it in there sombody ownd the car for 15 years before I got hold of it.

The monovalve on a W126 is between the 1st and 2nd firewall between the battery and the computer.