I just still don't understand why the overall tone continues to imply that the owner of the motorhome has more responsibility for understanding the proximity of the oil and coolant lines near the water pump than the repair shop.
I agree that it is unlikely that the repair shop in question will step up and take any responsibility but I completely disagree that the owner of the MH should just forget about it.
Tell your friend to file against them in small claims court. It doesn't cost much to file and you do not need a lawyer. You do need to bring compelling evidence of neglect on the part of that repair shop. Pictures of the damaged radiator fins and as much documentation from the other repairs shops as he can obtain would be good. Hopefully he still has the work order from the water pump and oil/filter change.
Let the court system sort out if they have any blame, not this friggin forum.