You cannot go wrong with the Allison Tranny. Just make sure that the filters were changed @ 1st 5000 mi IF required.
Dan the RV man makes a blanket slobber tube statement that does not apply to all rear radiators - case in point is our 06 Knight which was bought new. The 1st time out oil film on the radiator and tow car.
Cause - overfilled engine. Solution - Obtain correct oil fill capacity (inc. oil filter)from Cummins with your engine ser#, Change oil and filter, prefilling filter. Mark dipstick with file. Radiator has remained dry since and ISC does not use or drip any oil between yearly changes @ ~6000 mi.
Do have to rinse off dust from radiator yearly however, which is easy as the Rad and CAC are stacked.
Rig is for sale by the way.