The last one of these I had in order to fix I had to disassemble all the hoses and completely clean them. After that the unit started working. The case sensor was the right part to change, after that I would clean all of the hoses, including the one that connect to the case sensor. If the problem persists then the PBA (main control).
Here's another image to maybe under stand how the diode functions. The diode works by not letting the voltage back flow to the other valve that's not getting activated. It is working kind of like a check valve in this situation. The voltage goes into the diode to the valve, but unlike a connect, it doesn't allow voltage to flow through to the other connection. I may not be explaining it properly , but hey, I'm not a teacher either.
I've seen this challenge on numerous Samsung refrigerators, and I always order a new rear panel before repairing, even though sometimes customer always seam to say, "I saw a YOU-TUBE video and they didn't have to replace it, they only cracked a little bit of the styrofoam, are you not that talented?"
No, I'm that talented, I can remove it and only break a little bit of the styrofoam, I just don't want to have to come back and charge you again because you wanted me to do it and it caused the same problem. Then you would say I didn't fix it right the first time because it still had the same problem a few months later...
I agree, replace the entire assembly, if not you're asking for problems. That seal comes with the assembly, lube it with little bit of rinse aid to help get it down into place, but it's actually a pretty straight forward repair.
Sounds like you have a cooling problem in the Freezer, if there was ice buildup only on the upper right of the evaporator, there is a sealed system problem (leak). I may be off a little, but I think that most WPL Ice makers will not harvest the cubes unless the bimetal in the IM is below 13 degrees.