Final update on my quest for a good gasser. I looked and looked for a good 400E within a day's drive of me here in Boise, but to no avail. Along the way, nice W126's kept popping up. Here on the board, and elsewhere, I kept hearing how good the M117 engines are, 300K-400K with nothing to worry about except timing chains every 100K or so. In the end I fell for the siren song of the W126 and bought a really nice '86 560SEL from a nice retired gentleman only 5 minutes from my house here in Boise. The car was not advertised, and I found about it only through my local indy who knew of a nice 560 that might be for sale. The rest is history.
72K miles, books and records, always garaged, almost showroom new with the only issues related to having sat for so long being hardly driven. A few dried seals and gaskets, OAT gauge inop, rear suspension accumulators tired, and that's about it. All original right down to the Becker radio. Paid about what a similar condition 400E would have cost me.
This car is fantastic. I took my family around for a drive yesterday after I bought it, and my son told me to start the car so while he was adjusting the rear seat recline he wouldn't run down the battery (trained him well

). But the car was already idling! It's that smooth

. It almost just glides around silently and effortlessly like a magic carpet. After years of being away from gas Mercedes', I had almost forgotten what a delight they are.
So here I am right smack dab back in the V8 gas Benz business and loving it. Thanks for the advice and great discussion.