sorry this is so delayed. (I didn't realize you guys had kept this alive until I got an email update about a PM this morning)
This has to be one of the oddest things I've encountered in my time wrenching.
I've been fighting this with no good solution.
Typically my CEL would come on, along with VSC etc.
When I pull the codes they indicate the one or both rear 02 sensors
Knowing the situation with my car and the fluid wicking…
I change my 02 sensors (both rears) and spray electrical cleaner in the ECU connectors under the glove box.
Then i reset the check engine light, and also do a zero point calibration (to eliminate the VSC stuff).
This process usually last me about a year, and I can get o2 sensors for under 100 online each.
But I have changed my approach a bit this last time. Instead of OEM style 02 sensors I used Bosch universal fit sensors bc they create another connection point for the fluid to have to pass through (effectively another plug in the system). I don't know if this will help or not… I've only been running this way for about a month.
My last ditch thought was to re-pin the entire 02 circuit from sensor to ECU to by pass the transmission harness all together.
But the information in here about the transmission vent is interesting. and not something I have investigated.
But I will not spend 3-5k to replace a transmission harness / ECU on this car.