Thanks for the comments, guys! I was working on the machine all this time.
The service manual was quite helpful. Basically, I removed all the pumps from underneath the machine. There's an access panel. I checked for stuck pieces of anything broken, and found none. These are:
1) The drain pump.
2) The circulation motor (drives an impeller in the sump, and the waste "disposer" blades).
3) The distributor motor (drives a "valve" mechanism, I think, inside the sump area).
I also checked that sensor case, when I got it removed. There weren't any tricks in the service manual for this, it's just very fiddly to remove. It had enough gunk in it that this might have been the cause of the 9E errors (low level, I think). It's clean now.
I'm coming to the conclusion that either something isn't working at all (perhaps that distributor valve), or the seals are not doing their job. The whole inside of the sump area, underneath the filter was disgusting, with caked on brown gunk. The walls and every part of the machine is covered in whitish deposit of some sort. Maybe it's soap scum, but it's very dirty looking compared to the inside of a family member's much older Bosch (also with a stainless interior).
I'll didn't take any pics, unfortunately, but the seals I am worried about are described by Sears partsdirect.com here:http://www.searspartsdirect.com/partsdirect/part-model/Samsung-Parts/Dishwasher-Parts/Model-DMR78AHSXAA0000/1482/0130000/50039656/00004http://www.searspartsdirect.com/partsdirect/part-model/Samsung-Parts/Dishwasher-Parts/Model-DMR78AHSXAA0000/1482/0130000/50039656/00005
The enlarged images from those links are attached. In the first diagram (what Sears calls the base) you'll find part 3, the case assembly; and part 2-5, the sensor case. I had trouble separating the two, and trouble getting the two pipe fitments off from the rear of each.
The seals are listed in the second diagram (that Sears calls the pump assembly):
- Part 6 from the pump assembly: filter seal.
- Part 11 from the pump assembly:
From the same diagram:
- Part 10 is the impeller, driven by the circulation pump (or "pump").
- Part 8 is the valve, driven by the distributor motor (or "synchronous motor").
- Part 24 is the drain pump.
Those seals are next to impossible to get back in their "track" for assembly, so I'm guessing I stretched them during cleaning or something.