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?

And while we're on the subject, are transmissions from 2nd gen Legacys a close to straight bolt in swap (assuming I get the torque converter that matches my transmission)? 

 

Seems like they're pretty easy to find for under $200 here and the transmission that is the subject of this thread has over 200k on it so I might just swap in a known good lower mileage unit and then rebuild this to have on the shelf for when one of the other cars needs it.

I can not help you on the no reverse problem. That happened to one of ours and I just swapped the tranny.

If you go shopping for a transmission, there is a sticker on the bellhousing above the starter. Write down that code. The first 6 digits are very important.

The code on our 4EAT is TZ102Z.

Ask them if they can drive out the roll pins and leave the axle stubs in the tranny differential. Otherwise you will have to reuse the ones from your old tranny.

1 hour ago, arse_sidewards said:

I didn't see anything about voltage in the FSM

It will be in the auto trans Diagnostic section.