I have concerns about what OP stated. Several months of transmission issues resulting in 6 fluid fills equals roughly twice a month for 3 months. That's a lot. What does the actual symptom "clunky" mean? Depending on the description of symptoms. I recall a common issue of slipping gears 2-3-4 as a known issue. We may be able to point you in a direction. Is there any fluid on the ground? I believe leaks are likely to around the torque converter area if there is indeed a leak. I'm suspicious of dealer service as many people have told about misdiagnosis before. Any around the radiator area? If not, have any plastic panels been pulled off the underside to reveal leaks? How many miles on car? Used trans from a low mileage car is an alternative as mentioned. But because there is computer control involved, that needs to be looked at as a cause. An independent Asian car shop would be a good second opinion. Just give them your symptoms. They will also be able to look for trouble codes. Toyota should have done this already. We want to help you.