Replace that $400 sender, not the O ring. Tulsa heat kills them.

Damn, that sucks, a cracked holder with zero warning is every machinist's nightmare.

That 60 ft lb number is where I have to push back a little. On an ER32 nut the maker's spec is usually more like 70 to 80 ft lbs for full grip, and a lot of guys run them lower than that and wonder why the collet spins. The real problem with your pipe is not so much that the nut needed 60, it is that a 4 foot pipe turns any normal pull into a guessing game, since where you grab the pipe changes the math. Dayton guy was right about the taper though, side load on the nut is what kills the spindle nose, not the torque itself. Good call on the proper wrench set, just check the spec stamped on the nut before you set the wrench.