The Allison team that did this design was a great crew. I was very involved in the lab testing. By the late 90s we had a good understanding of what it took to validate life on a transmission intended to go many hundreds of thousands of miles. It was a lot of expensive and lengthy tests, and the investment paid off with good performance in the real world.
The control filter is essentially a bypass filter, although it does not have super fine filtration that typically is associated with engine bypass filters. The individual control solenoids have mesh screen filters built into them, but this is a bit finer and easily replaced.
It's a level of maintainability that you would not typically see in an automotive unit, more like in a medium truck/bus transmission.
