For the record, the modulator is on the Driver's side (Haasman's reference to the "left" side might be confusing to some.
Also, the caps vary in color depending on which tranny is installed. Haasman and I have black caps on our respective modulators, but there are also versions with other color caps (i.e. green.)
1991 560SEL-Euro (145,000 miles)
1989 420SEL (Retired at 325,000 miles)