I drive School Bus for a large School District. The Bus I drive is an 84 Passenger 1997 "Bluebird" with the CTD 5. 9 12 Valve 275 HP Engine, and it has the Allison 1000 5 speed automatic, very similar to the ones used in the Duramax. We have been experiencing converter oil leaks in most of them, particularly when they start getting over 50,000 miles. Mine was one of them that had to be repaired with under 75,000 miles.
They are not hard to repair, as the converters are in two pieces bolted together with a seal between the pieces. Biggest headache is removing them from the Bus!
Wayne
amsoilman