Well, the 1988 560SEL with 215k made it the 4,500+ miles from Phoenix to Buffalo and back. I used Shell Rotella 15w-40 diesel oil for the trip. My back and tailbone are absolutely killing me from the stupid seats. I bought a memory foam seat pad in Buffalo at a WalMart to use on the trip back, which worked, but was still very uncomfortable. I actually stopped by a pool supply store while there and bought two giant pool noodles, but never got the chance to install them in the seat. So basically I bought pool noodles in Buffalo and brought them back to Phoenix, the pool capital of the US. Oh the irony.
No major problems with the engine or tranny, but lots of little annoying electrical gremlins. The SRS light would keep coming on until it went solid. The ACC unit would not regulate the temperature at all, just fan speed. There wasn't any heat at all actually, even though I just replaced the mono valve. I'll have to look into the aux water pump soon and the ACC unit as well. It was working just fine earlier this past spring. My recirc button isn't working now either, which may indicate aux water pump problems so I've read. I shouldn't complain though as my r134 conversion A/C was super cold and didn't go out the whole way. The "light-out" idiot light kept coming on at the end of the first day, so I got out the soldering gun in Albuquerque and went to town on the major soldering points on the control module in the hotel room. I got the right rear tail light to stay on, but every once in a while during the rest of the trip, either the left or the right headlight with go out for a second and then come back on.
Not once in almost 5,000 miles did I see another older Mercedes on the road. Not a thing. Kind of sad really. I did spot an older light blue w123 in a suburb of Buffalo a ways behind me at a light that I just happened to see in my rear-view mirror.
I have just one major rant. What is the deal with all the new semis/18-wheelers and some new cars with BLINDINGLY bright blueish LED headlights??? How are those legal? Also, Indiana still has the worst roads and freeways. Though, even with Google maps telling me EXACTLY what to do, I still took the wrong freeway turn in St Louis and had to re-route. Damn you St. Louis, you got me again! At least this time, I didn't end up taking the wrong bridge like last time, which dumped out into the north side of downtown, making me have to snake back south to the correct freeway.

Stops (including start and end points):
There: Phoenix - Albuquerque - Joplin - Columbus - Buffalo
Back: Buffalo - Brazil, IN - Shamrock, TX - Phoenix