I get a light on my dashboard occasionally that a light is out. It's always the right rear side marker...... always.

I've previously scraped off any calcium buildup (or whatever that stuff is) on the metal bar that holds all the bulbs, I've changed the bulb, plus I've put dielectric grease on the bulb base. It works sometimes, but then I get a notification on the dash and..... it's the right rear bulb again.

I had my mechanic look at the car. The dash indicator light came on. I told him it's always this right rear side marker bulb. ....always. He looks and.... the bulb is working fine.

So he looks around the rest of the car and this time it was the FRONT LEFT marker this time! I replace the front left bulb a few days later, it's working fine, I start the car up.... the right rear bulb is not working again plus my left turn signal light stays on constantly (not blinking) on the dash.

What is up with this? How do I fix this?

1991 300d 214k