BAD BAD IDEA
I have a good buddy who works at a local "auto recycling center" (aka: junkyard) and he tells me he consistently see's W140 S classes come in that run and drive beutifully, but have so many little problems that there owners get fed up and sell them. He sais that early 90's armored cars are especially plentiful because not every armoring company can make a dependable product. Think about it. They take the cars apart, and add heavy "hidden" armor. Then they screw it all back together again. I would not trust the company that armored your Mercedes considering they added all that extra weight to an already weezing M104 engine. The first chance I got, I would dump that car onto ANOTHER unsuspecting owner. This car will cause you nothing but headaches and debt!
And, if its an armored model, the rear windows might not move. Many armored cars rear windows dont move so the passengers cant be placed at risk of a well planned attack. Even with the new W220 S500 Guard, power rear windows are a costly option. Find out who armored your car buy checking your doorseals, hood, trunk, etc. for the companies decals; and do some research on your car!
"If I teach you half of what I forgot, you'll still have enough to compete with most people"