Thanks T.G. and Guenter for your replies.

I found a car spare part shop around my neighborhood today and
Mercedes are their speciality. I talked to the guy in charge about the
Mercedes I tested and he said that a 300E is such a popular model that
when it comes to body parts I'll always find them around, and since
it's an '89 they're not expensive. He said the only parts that might
end up costing a bit more than its equivalent for a newer Asian car
are some electrical components (motors for electric windows, mirrors,
sunroof, etc.) or engine parts (which I'll make sure this Mercedes
won't need since it only has 35K miles on it). I told him that the
owner of this 300E mentioned two things that needed repair: 1-The A/C
system was in perfect condition but needed a recharge, and 2-The
little thingy (motor?) that moves the windshield wiper was acting
funny sometimes. He said that the A/C charge was cheap and any repair
shop could do that, and that the windshield wiper motor would cost me
like $115 (not bad!). Labor cost would always depend on what mechanic
I chose, obviously.

He did mention that the only two possible disadvantages to buying this
car are that it's a big engine (to which I'd have to adjust to more
intelligent driving habits), and that being an '89 it'd be harder for
me to sell it later. I really don't see any of these two as big
problems. I've never been a "pedal-to-the-metal" kind of driver, and
besides there are so many traffic jams and pot holes everywhere around
my city, it's almost impossible to find the chance of speeding. And
about selling the car, I don't think I'd end up feeling the need to do
so. It's a gorgeous car in great shape and old enough that my
insurance costs drop significantly. And like the spare part shop guy
said: "If you're gonna get an '89 300E in such a great shape with only
35K miles on it, you'll want to keep it for at least five years."

So I'm pretty much sold on it. I'll try to get a mechanic to check the
car throughly and if it passes the inspection I'll buy it.

Sergio,  just so you are aware.  The engine is not that powerful... you
may well end up being a pedal to the metal kind of driver since the car
will always start in 2nd gear, unless you shift yourself from 1st (marked 2)
On the other hand, it does save considerably on gas and sure helps in winter
on snow and ice if that's the case

cheers, guenter

ps.  I'll never sell mine