Ford 7.3 diesel new motor really?

I have a 99 power stroke 7.3 with 125k on it. It was having a rough start for a while especially when cold and would have almost no power until it warmed up on occasions when it was colder out and have white smoke from tail pipe until it was running warmer.

Fast forward to a week or two ago, still had some white smoke at start up so I decided to run some seafoam through it to see if it would clear it up, well about a quarter of a tank through one day while driving it was losing power to where it eventually died, no check engine lights ever.

Have it towed to a local dealer they tell me it reads at a 4 out of an 8 scale and they hear crankshaft noise, tell me it's toast, 13k for a new one installed…

Umm no thanks so I pick it up and drive it home about 20 miles on hwy and it acts like there was never any issue? Have driven it more often recently and has quite a bit of white smoke at start up and until warm but once warm drives like no issues, no lack of power at start up but its also warmer out, so i guess my main? Does this motor sound like it's shot from what I have described? If so it's hard to believe the way it's driving unless what the dealership described to me is the beginning of the end for this motor, thanks in advance for any advice/help

Something does not sound right I would have it looked at by another mechanic 125 k is nothing on that motor they typically go well over 200k