the internet is a great source for information;
per another forum, electrolysis does not erode, it plates, adding material. (In the days past, old style coolant flowing thru iron blocks, aluminum heads would cause aluminum radiators to clog). Cavitation erodes. All diesels have issues with cavitation, it is dealt with by every manufacturer with coolant maintainance. Gas motors ALSO need the coolant maintained.
Ford has a high tech engine in the 6.7 with aluminum heads and a compacted graphite iron block, the coolant is a fluid that requires maintainance as does the oil.
My 7.3 had 340,000 miles and was still running strong the day it was totalled. I maintained the oil using synthetic mobil 1, and maintained the coolant
(test strips are available at a good auto parts store), the result was a truck that still smoked the tires at 340k. Ford has a light that tells you the oil needs changed, a coolant message is posted when it needs checked. This assists people as your inlaws who were not aware of a maintainance issue, just buying a vehicle and driving it has responsibility beyond fuel. Sadly, dealers do not inform buyers of any make of cavitation, probably trusting buyers to bring their vehicles in for the scheduled maintainance points. Ford has stepped up the info beyond it's sales/shop staff.
A lot of auto mechanics that do not know diesels, are not aware of cavitation, as your inlaws were not. Diesels are tough work engines, high compression, close tolerances, that can take a lot of abuse and deliver gobs of torque. However neglect comes with a heavy price. You can trash Ford, and find the same problems with Kubota, Cummins, or any diesel with a Google search
. If Ford is the only manufacturer of diesels, you are correct.