More guesswork than knowledge, I'm sorry to say... Here's another thought: there was a problem with either the M40 or M42 engines, maybe both, something to do with the timing chain case or whatever, I'm sorry I don't have the details, maybe it was gasket material incompatible with the coolant. Do an Internet search using, for example, "BMW M42 timing chain" for starters, then refine your search as you find pertinent hints. Again, this is a stretch, in that a problem of this type would normally have manifested itself a l-o-n-g time ago, and whether it pertains to your issue I don't know, so this is just a thought.
As to the general condition of the world, I have even less to offer for possible solutions...