A person's ocupation...
...may be a good barometer of how well his/her car was cared for. As a general rule, I like to buy used cars from pilots, they are fastidious, to the point of being anal, about maintenace. they fully understand how critical regular service is. Of course, their lives, and the lives of their passengers depends on regular maintenance by well-qualified mechanics. Engineers are also a fuzzy lot.
I bought my current 1991 420SEL from a studio executive here in So. California. The car was lovingly and regularly maintained. If the car as much as had a hiccup, they would bring a guy from Germany to burp it (well, that's a bit of an exxageration, but you get the idea). Every maintenace item was fully documented and no expenses were spared (I guess that is why we pay such high ticket prices, the studios have to cover their executive's overhead). Now every time that I go to the movies and see this particular's studio's logo on the screen, I thank them for taking such good care of my car.
I guess the point is, that anyone looking to buy a used car should first look at the service history and second have an trusted mechanic give it the once over.
As far as specific items to look for, I'd say that the dreaded timing chain is the single biggest area of concern. Next are A/C issues, compressor, controls, etc. The radiator may need replacement because of the famously (or infamously) weak plastic neck. Fuel pump(?) fuel distributor (?) and injectors (?) may also be issues of concern. And, if you care to, you may want to repalce the stock Benz Becker stereo.
Remember that 1986 was the first year for the 420SEL, so it may not be the finest example of an otherwise great car. Other than that, the 420SEL, in my forever to be humble opinion, is one of the finest cars ever made by Benz.
PS. DRBRANDINI, I am glad that Jesus took nails in his hands. I am far happier when I let him do all the driving. I know that with him at the wheel, I'll never take a wrong turn.
1989 300TE "Alice"
1990 300CE "Sam Spade"
1991 300CE "Beowulf" RIP (06.1991 - 10.10.2007)
1998 E320 "Orson"
2002 C320 Wagon "Molly Fox"
Res non semper sunt quae esse videntur
Not in this weather!