You can have a look at:
http://www.mindspring.com/~houlihan/mb.htm

John M.
'94 E320 gasser

The internal condition of any diesel is appraised by a compression test.
So make that part of any purchase agreement; it costs a bit but will
avoid a lot of expense afterward.

I've owned a '80 300SD M-B diesel since it was new and have a few
opinions about diesels. The old, all iron motors (thru '85) are tough,
durable engines that can take a lot of use and abuse. Old, all
mechanical technology that lends itself to the DIY owner. The later
engines have better performance but are not as tough as these old dogs.

Yes, some engines have lasted for vast mileages but those were
fastidiously maintained, perhaps over maintained. IMHO the useful life
of a reasonably maintained all iron diesel is about 275K miles +/- 10%
after which it will need an overhaul, probably the transmission as well.
The newer motors' iron blocks and aluminum cylinder heads may need a
head gasket before they reach an overhaul.

As to fuel economy, the old 300SD consistently delivers 24 mpg in
commute driving. Notice the diesels' relatively high city mileage for
it's their main benefit, a reasonably sized gas engine will approach
diesel mileage on the open road. My '97 E320 which has much better
performance achieves and 26 - 28 mpg on the road, about the same as the
old diesel.

M-B will be selling a new E320 V-6 diesel starting in October. This
motor has better acceleration than their 3.5L V-6 gas engine and the
diesel's mileage is about 33% better than the gas motor! Both of these
motors are "state of the art" producing 75 HP/L and I relate this so you
see what can be achieved. But this new diesel is more complicated than
its V-6 gas sibling and that forsakes the diesel's traditional
simplicity. I'm thinking about buying one but am quite wary of its
complexity.

You should know that the diesels require more frequent oil and filter
changes than do the gas motors - it varies by engine so check that
before you buy. Diesel fuel now costs more than premium gas (San
Francisco Bay Area) so the fuel isn't "cheap" and it will head higher
when the sulfur is removed this summer.

A diesel helps but it isn't the magic solution to high fuel costs; that
can only come from lighter cars and smaller engines.

The MBUSA site has a menu of "prior models" that may help your
investigation.

An engine.

You are on the right track. Full service record is a plus... Have a MB
diesel mechanic look over the car... dealer might be your best bet for
overall checkup unless you find one locally. Do this before you buy the car.

Check the tranny operation... is it smooth and responsive?

You really have to test drive them. I got a 1995 and I love it.

I seem to be getting hauled along on Mercedes hunts these days when a
friend wants something to run on bio or a big, safe car that gets good
mileage. These are some of the instant disqualifiers. If I see this, we
move on to the next car without even bothering to take it to the MB
mechanic:
--Torn CV boots. CVs ain't cheap and they can be very expensive if
you have a shop do the work.
--Water in the trunk. It has been my experience that this is the rear
window seal rather than the trunk seal. That means there is probably
some rust happening around the window.
--Make sure the cruise control works. Otherwise you are looking at
around $300 to have the amp and the actuator rebuilt.
--Keys. Get as many as you can from the previous owner since dealers
charge up to $50 each to copy them.
--Rust. Get under the car and look. They are usually old. That means
even if you are looking at a car in AZ, it might have lived in place
that used salt on the roads.
--Gauges. Make sure all the gauges work. Odometers tend to be shot.
This might tell you how much stock you should put into the odometer
having actual mileage.
--Open the oil filler cap on the engine and see how much vapor is
rising when the engine is running. This gives you an idea of how bad
the blow by is without having to do a (much more conclusive)
compression test right away. Btw, a worn diesel engine may run very
well. Don't mistake easy starting and smooth running as signs of good
engine condition.
Here in the PNW, a good 123, 124, or 116 body with good interior goes
for about $500 with a bad motor/tranny. If you fall in love with a car
with a bad motor, no matter how perfect the body/interior, remember
after getting the new/used engine in it, it will never be worth what
you have into it. You may think you're going to drive it forever so
it won't matter. And it won't matter, until some a.shole comes over
the centerline and turns your car into metal origami. What they gave me
for my mechanically perfect '83 300DT didn't even cover the price
of a good transmission.
    I'm sure others will have other things they look for as well.

    http://articles.mbz.org/buying/checklists/124/