FastLane shows a 98 S500 takes F8DPER plugs. R usually means resistor plug. I believe the F8DC4 plugs go into early M119s with distributors and plug wires. I suspect in the coil over plug arrangement there is no wire to serve as a resistor.

FWIW when I got my now sold 95 S420 with 125K miles, it had MB logo Beru 14FGH-8DTURXO plugs (I keep one beside my PC). I don't know if R means resistor plug in Beru-speak. It bogged when accelerating hard over 4000rpm. Switching to F8DC4 plugs didn't help. What helped was a set of new cap$, rotor$ and wire$. In fact I didn't notice any difference in performance between the Beru and Bosch plugs.

To H-guy's point, don't get exterior bulbs at an auto parts store unless you want to confound the illumination warning system.

Sixto
93 300SD