Help is coming for the 1982 to 1989 R107, the 1981 to 1985 W123 and the 1981 to 1991 W126 with ACCIII.
They are old and they are tired. Even the newest model is now 30 years old. If you own one of these cars, you might agree that your systems “works” most of the time but sometimes, not so good. In the past you probably replaced the mono valve and things improved. At least you were getting hot when you wanted it and could turn it off when you desired. But now you find out that Bosch is no longer making the mono valve replacement and your system is acting up again. There are a lot of Mercedes still on the road that suffer these maladies.