The 1997 models have coil packs, so there's no distributor/wires. If the engine is only firing on four cylinders (you don't mention which four) I would be looking at something more nefarious, such as the engine wiring harness being shot.

The W140 is a very complex car so it may be worth it to have the car towed to a dealer or indy shop and having a pre-purchase inspection done. It will cost you a couple hundred bucks, but you will be going into the deal with your eyes wide open.

__________________
"It's not about how fast you can go, but how well you can go fast."

Bob in Richmond

'97 S320 (LWB), Ruby Red Metallic, 73k miles
'97 S420V, Smoke Silver Metallic, 155k miles