I'm guessing you're stuck with the truck and paying for the motor, at least if it's like any vehicle I ever bought you bought it as is, where is no warranty expressed or implied.
Without knowing the Whole "back story".. I'm guessing you have got yourself some valuable (& expensive) experience.. Oh & some tax deductions you probably Don't really need or can Afford........ Welcome to Truckin'.......
LMFAO! Clackety Clackety Clackety. My dad bought a Buick station wagon brand new in 1984 with that diesel in it. They were a colossal pos brand new. 350 cui of raw American power. 105 hp. 0-60 in 21 seconds. Lol. Leaked fuel so bad from the factory they couldn't even put them on the show room floor.
Mine was a v6 diesel but just as much of a boat anchor as the v8 was . Finally traded it even up for a Ford garden tractor with a bad engine and think I got the better end of the deal .
I tell as many people as I can to stay away from anything that says Paccar, Cummins, Peterbilt, or Kenworth. Just like anything, when it’s new, it’s fine. Put some miles on these things and they’ll eat you alive.
It's too late to do what should of been done. That is give the truck a proper inspection yourself, it's your responsibility when buying one no one else's. All you can do at this point is fix what you have and go truckin