I have the same 2007 classic dually with 160K on the clock.
Unfortunately my thoughts are the same as Burbman's. If the unit needs to come apart. It's time to consider rebuilding.
I had some overheating issues this past summer that were resolved, I was advised by the local Allison guru that if the tranny needs to come out it's time to rebuild plain and simple.
I feel like I dodged a bullet but now I know there are really no simple inexpensive fixes. Once the unit is removed and opened a rebuild is in order. I was quoted $3000-$3500 for a upgraded bullet proofed for towing rebuild.
