If they don't have it in the records, you can pull back some of the insulation on the harness to see if its degraded or not. Most cars of that era have had to deal with it by now, so I doubt you'll see many original harnesses.

I love my diesels, but feel just as confident with a M103-104 going 300k plus as well. The gasser engines don't tend to be nearly as leak prone or get really dirty either. Just like with all Mercedes though, even if you buy a nice ones there's always a 1-2k of stuff that it needs.

Here's my short criteria on an average wagon you'll come across with 80- 150k in nice cosmetic shape.

The most I would pay for one is $6000, and I would deduct...

$1500 if its the original wiring harness
$1500 if its on the original head gasket
$3000 if its devoid of a good service history, fluids look old, etc.
$1000 if its the original Evaporator (even though I priced it at about half of the job would take its about a 50/50 shot you'll have to deal with it unless you keep the car for a very long time.

A PPI will also bring to light if the rear hydraulic suspension is getting weak, or the front end is starting to have issues.

If you have not seen this little gem in the sale forum, I strongly suggest you consider it. Its a very good price considering what has been done to it.

http://www.peachparts.com/shopforum/showthread.php?t=261593&highlight=e320+wagon

I bought my '95 E320 with 148k in very nice shape for $2500. It had a great service history, including a new wiring harness, but the original head gasket was leaking, and it still had the original (still good) evaporator. $2000 later I had a very nice, well sorted, turn key wagon.

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1985 500SL Euro w/ AMG bits 130k
1984 300SD Turbodiesel 192k
1980 240D Stick China 188k
2001 CLK55 AMG 101k
2007 S600 Biturbo 149k Overheated Project, IT'S ALIVE!!!