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The TSS and ISS and OSS can withstand temps over 350 degrees. Transmissions operate at 200 degrees, transmission seals fail at 250 degrees. If the transmission is not ruined and totaled then its not getting hot enough to melt a seal. To melt a seal you must a external heat concern from the exhaust or the tone ring inside the transmission is hitting the sensor and grinding the head off the sensor.
There is something else going on here, there is no way a transmission could survive after getting hot enough to melt sensors. much less its only affecting the TSS when the OSS and ISS are the exact same material. Have you actually hooked up a scan tool and watched the fluid temp sensor to see if the temp is actually high or not.
For the Carrier - planetary gear overdrive (with trigger wheel) to wobble and hit the sensor the center support has to have bushing damage or the front carriers worn out and wobbling.
If the trans gets over 240 F the dash will warn you. Its gonna take over 300F to melt plastic. Regardless of what you decide getting to hot or the sensor being hit, its gonna need to come out and get overhauled, Below are some pictures.
Disassembled view down loadable here