The Title says it all. New plugs, foul (black) quickly. Lots of blue smoke. Seems to be gasoline dripping out the tail pipe.

Sounds like its burning way rich and something wrong with your fuel injectors or something. Alot of people know about the W126 V8 and I am sure will respond soon with more info that I could ever know.

Hang in there.

Blue smoke is oil. Black is gas. The dripping is probably water, from your catalytic converters turning burning oil into water and CO2 as fast as they can trying to keep up.

Depending on miles you're probably due for valve stem seals and possibly valve guides. Could be just a gummed up PCV valve but of course we can't diagnose everything over the web! Obviously check that first, it's a cheap & easy fix if it's the problem. The bottom end of the m117 is a durable beast and unless run low on oil or the oil wasn't changed for a very long time, you're probably still in great shape.

FWIW you may want to check timing chain stretch and do that with new top guide rails at the same time.