That would be me in post #2. Damn I’m good. (modest too)
Sorry about the $400 bucks, I know how it sucks to have to spend money you don’t have.
As far as your friend goes, was the engine run at all after the mis-fueling? (even started?)
If the answer is a firm no, then all that has to be done is to drain the fuel tank, and fill it with the corect fuel.
If on the other hand the engine was run, at the very minimum it will require a new fuel filter. If on the other hand, the engine was run till it quit, things might get a little more serious.
I have drained the tanks on dozens of misfueled diesels, and never had one with engine damage, but it can happen.