Let's see.. ever since I've had mine I've had to do:
Evaporator *ouch* (recently - lots of $$$)
Wiring Harness ($900 parts and labor)
Front Brake Pads (but then again... its brakes are really good and it accelerates quickly, maybe if I drive slow it wouldn't have needed new pads up front)
Motor mounts ($300?) dont know why I had them replaced when they were still good.
Crankshaft Position Sensor (car was cranking for long periods of time)
Starter Motor (odd one, nobody ever heard of a starter motor failing on a 119 engine)
that's it... under my ownership. The previous owner spent thousands of $$ though (i have all the receipt) in maintenance, regular detailing, tires, etc. - so the car was very well maintained.
other than that.. just lots of detailing
looks as sharp as ever
http://209.150.52.134:2000/e420/
Why I like the E420 (let's not put the 500 in the picture
)
The motor just sounds amazing and it's very smooth. I'd say the E320 is not much slower but they are only $1000 cheaper at most.
When I was buying my 124 - I knew that I wanted either a V8 or that I-6 Diesel (E300). The coupe E320 being an exception.
I think the best thing is to buy one that has had its evaporator replaced because everything else isn't so bad.
regarding fuel mileage, mine constantly returns 15-17mpg (90% city driving)