I ran into this problem last year with my 335i's engine that self-ventilated through the bottom and took out the steering rack at VIR.
We went through 2 used engines that were complete junk before we decided to buy a new N55 from BMW. Only then was it good to go.
This experience will also affect the make/model of vehicle that I purchase next. At this point, I'm only considering domestic brands because when you have a catastrophic powertrain failure, only their replacement part costs are low enough that it wouldn't be worth my time dealing with the hassle of a used engine/transmission.