I had a similiar experience with my 97 C230.... would not shift into fourth.

Cause = I was way low on transmission fluid.

I had consulted several "experts" and everyone told me that low fluid would not cause such a situation. Well, I changed the fluid, put in a new filter and transmission was "normal" again.

When you check your fluid level >make sure car is on level ground, transmission fluid is at "operating temp" = 80C [trans fluid temp >>not necessarily coolant operating temp] I use an infrared thermoter > ping the tranny pan to get tranny fluid operating temp.

If it's not fluid level that is causing the no-shift situation > then it could be transmission "valve body .. K2 " > I have no experience with these components.