A fast turn signal on one side is usually a failed bulb or socket. The 4 way flasher can get dirty and cause problems but usually to both sides. A flasher does not know which side is blinking so a flasher or relay is unlikely. Put on the 4 ways and walk around the car, a bulb, front or rear is most likely the culprit. All bulbs should be the same brightness and blink at the same rate.

__________________
81 300CD (sold) 1972 280 SEL 4.5 (sold) 1966 250 S 4 spd (sold) 1974 450 SL (sold) 86 BMW 325ES (sold), 1973 280C (sold) 1988 300 SE.