Blinker problem

Hi everybody: I am a new member here and I own a 1995 S420 that has a blinker problem.  The left blinker is blinking really fast and the bulb malfuntion indicator in the dashboard is on if I use it.  I took it to a non-dealer mercedes shop and they tried to replace both bulb (front and back blinker) but it is still doing it. None of the bulb is burnt though.  They told me it is either a relay problem or the electric and I was quoted of at least 200-300 for it.  If anybody can help me with this, I really appreciate it.

Thanks - Benny