Identify what transmission it is and get a deep aluminum pan for it. You can have the new pan drilled and tapped for a temp probe when you order it, and it will have a drain plug in it, so future fluid changes and pan removals are much less messy and easy. New deep pans can add as much as 4 qts to the capacity of the transmission which goes a long ways in keeping it cool.
I can suggest one place www.Yourcovers.com as they are quite nice and easy to deal with. For this transmission, there are probably several companies that make deep aluminum pans. For the transmission in my Sprinter, PML (which is www.yourcovers.com) was the only one. They have a very broad line of pans. Make sure you know what year CHASSIS the coach is on, probably the year prior to the coach.
Charles
