I have a 1990 BMW 735i, about 150,000 mi. One side (left) turn signal blinks rapidly, other blinks at a normal speed. Tried a new flasher, not it. All bulbs work. Have been told it may be a "contact" issue, but how do I solve that? Have removed all bulbs/sockets, cleaned and replaced them. Ideas?

BMW cars need 21 watt silver base original equipment
light bulbs for turn signal/marker lights.
Try this and repost if needed.