hi michaeld and all
It's actually much
worse than what michaeld describes. Even if the new cars have/had some accessible components, the DIY maintenance is now virtually impossible.
In another thread, I was trying to help oscar with his injector 4 and 8 problem, my last post suggested using an oscilloscope to "see" the pulse train. That is as bad as it gets with a W116. A cheap multimetre with a frequency counter range would also do. But that is
not even a starter on the "new" cars.
To simplify, the "new" car creed is something like this: if a mechanical function can be turned over to "silicon", do it ! the physical part is cheaper to manufacture and you can tell your clients that it is modern "digital" stuff when they complain about the (inflated) price. People are suckers for anything "digital"...
So how do you do DIY work on the "silicon" ? either you don't or you
become a mechanic 
Here is a case in point : a few years ago, I was working on a training program for Renault. A collaborator named Richard who lived in Nottingham, UK was helping out with documentation.
To "fix" a Renault, like most "new" cars, you plug a laptop computer somewhere and run the diagnostic tools, etc. For a Renault, there is a
special laptop named
Clip, specialised laptops are the norm so any old one will not do

, and a software pack allows one to see everything including all the data transiting over the multiplexed network and the several custom micro-controllers and up to the "central cabin computer". Wow, a new Renault has a "central cabin computer" all digital and all

So Richard had a Ford Mondeo and I asked him how he got data from a Renault. He said "Well, my neighbour in Nottingham has a Mégane and she lets me plug into it ever since I showed her that I had "fixed"
14 problems...I explained to her that there were
mistakes in the data for fuel injection and the climate control and that I had corrected them by entering the right data and updating the software in the FI "computer" with the lastest service CD" and she said : "Oh...but... I didn't have any problem..." and Richard replied "...you were ABOUT to have one with the fuel injection, the data errors that would have increased your fuel consumption quite a bit."
The lady was sold ! Go ahead mister Richard, "fix" my car as much as you like

Some of the problems came from electrical glitches or buggy programs. Yes, "new" cars have
BUGS, isn't technology wonderful

Personally, I will simply NOT put up with cars that behave like poorly configured Windows PCs. This makes my choice of "new" cars stop at the early W126 cars.
Aside from the dashboard and pneumatics, I consider my W116 to be a joy to maintain and with the M116 engine, the easyest to access in the engine area. Even the steering box adjustment is accessible between the third and fourth branch of the left exhaust manifold.
As to the very easiest car for DIY, I firmly believe that a W123 240D is utter happiness on wheels with a star to enjoy.
Bugs belong in computers not in the cruise control or ABS !!!
Denis
Paris, France