Hi Brad,
After we purchased our '06 Thunder from Bend, we had the leak start on the first trip. The guys at Bend ask that we bring the rig back, as a change out was required. It's a big job, and the new radiator was very expensive. The total cost was around $12,000, of which the radiator was 9000. If you need to change out, make sure you get a shop that know how to do the RV work.
The Guys in Bend did the total change at no cost to us, as our extended warranty refused to pay any of the bill, claiming that the problem was preexisting.