Just to confuse the issue, here is my two cents:
When getting my ATX aux-cooler installed my tyranny man said that the fluid in a transmission will perform best when warm (not hot or cold). The transmission is designed to run at the engine radiator temperature. Therefore, running the output of the aux-cooler through the radiator serves the purpose of maintaining the ultimate temp for operation. Don't forget those COLD winter days.
AND: if you are getting metal flakes in the filter.. you need repairs made to the transmission.
Gray colored dust is normal and comes from clutch material.
