1994 E420.

Check out this LARGE PICT. You're looking at the first three plujs from the passenger-side bank. Why are they covered in oil? What do I need to replace....valve cover gasket.

aside from that, how do I tell if I need new plugs? The car starts pretty heavy (cranks a bunch of times before it actually starts).

Common issue on all double overhead cam engines (DOHC) where the plug enters the chamber between the valves. There is a small "donut" like gasket at the top of each plug well that is accessible when you remove the valve covers. Oil slips past these gaskets and fills the well. I've seen them filled almost to the top on some cars.
If the valve cover gaskets are old, replace them along with the "donut" gaskets. Obviously, there are 8 of them... change them all.
While you're in there, you can check your chain slack and oil tubes.

__________________
KenP

1996 S500 W140 Coupe

cool, thanks. Probably will have to change the valve cover gasket in the process right?

I believe a new valvecover gasket set comes with the o-rings for the sparkplugs.
Have a look at the picture at FastLane.
Look under " Engine- Mechanical " valvecover gasket set.

__________________
2007 C 230 Sport.

Vehicle: 1994 Mercedes Benz E 420
Part: Valve Cover Gasket Set
---------------------------------------------------
Valve Cover Gasket Set
Left
-------------------------------------------------
Valve Cover Gasket Set
Right

http://63.89.49.212/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1R3040FWM1RB0O6NQG&year=1994&make=MB&model=E-420-001&category=A&part=Valve+Cover+Gasket+Set