I think you are right that this happens TriX5. I'm sure people get advice to have transmission work done and decide just to unload the car. I know I considered it briefly when mine started to exhibit symptoms.

I think people also try replacing half their ATF and then add in another fluid of different viscosity. This likely isn't very good for a transmission. To replace all the fluid, you have remove the transmission and drain the torque converter. As we know this is no small task.

My particular problem was a very slow oil leak at the bell housing. It was just accumulating underneath the transmission oil pan and there was no fluid hitting my garage floor, so I wasn't too worried about it. Then one day when it was cold, the torque converter didn't want to lock up for about 10 seconds. I was giving more throttle and the engine just revved higher with no acceleration. Then it locked up and I drove home.

I did some reading and figured out this symptom is consistent with a torque converter seal leak and a gradual decline in the ATF level. At some point, the torque converter won't look up consistently if the fluid is too low.

I almost have the transmission out. I plan to inspect the debris in the oil pan and filter plus drain the torque converter. If there is anything more than just the usual shavings around the magnets, I will likely decide to do a full rebuild. For now, I'll cross my fingers ...

Anyway, my point is I must not be the only one with this very slow ATF leak. With no easy way to check the fluid level and no scheduled maintenance of the ATF, most people would be unaware of the issue. And if the symptoms are ignored, eventually the torque converter would self destruct and spew bits of metal into the transmission.