Thanks for the response! Do you know if there's any difference, other than oil pan, between manual & auto N52s? Realoem has an AT crank noted so we're afraid to grab a manual, but there's a nice one available locally.

And of course I'll post once we open the engine up. I got more back story on what happened. My friends said they were cruising on the highway and it started tapping. They thought it was lifter tap and were going to get off on the next exit. It started losing power, automatically downshifted pretty hard (4k rpm), and the engine almost immediately went boom. That almost does sound like bottom end to me (why else would it lose power?)... The most recent work done to this engine would be the fuel pump, CCV hose, intake manifold gaskets, non-return valves, spark plugs, coils, and air filter about 2k-2500 miles ago. Outside of what I noted in the original post, the engine has never made any weird noises or behaved oddly. It's been extremely well maintained and documented so it's frustrating to have such a failure occur, but I guess that's life.