Fluid is present in the proper amount and not burned. Shifter mechanism is working properly. All other gears work properly. Reverse doesn't even attempt to engage, hot or cold doesn't matter, it's like it's still in neutral. It worked fine yesterday.
I pulled codes and got 13, 24 and 33 (24 and 33 clearly don't have much to do with the reverse issue).
About a month ago I changed the transmission fluid for the first time under my ownership and probably the first time in a very long time. I assume that the new fluid knocked all sorts of stuff loose because it promptly plugged up the filter I installed at that time. Considering that I lost the gear with no warning and I'm getting solenoid codes I'm thinking that some of the stuff that got loose could also be affecting solenoid operation. Therefore the path forward is to drop the valve-body, clean the crap out of it, verify the solenoids are all working and reinstall.
So my questions are:
Is the valve body gasket reusable?
What is the OE O-ring and gasket material (I want to make sure whatever cleaner I use won't destroy them)?
Can I test the solenoids at a full 12v or do they operate at a lower voltage (I didn't see anything about voltage in the FSM)?
Anything else (other than worn out clutches) that could be causing my issue?