Hi
If you have a 722.5 the correct level to have good shifts is at MAX at 80 C .
I use infrared tolls directed on the oïl pan and when oïl is at 80 C you have to put hand brake ad gear in D. For security i also put wood in front of Wheel.
I have a CLK 430 1998 i think transmission is similar 722.5 and I have 300.000 Km with no problem.
This model had also some springs that broke Inside valve body but now i am not able to tell you wich exactly.
I think next step is inspect one by one springs on each side of valve body.
Your code is pressure control solenoid may be is just this one going bad.
Hope this help you a little