I've had a problem with mine and I narrowed it down to the socket.
I first tried cleaning out the socket due to a little bit of corrosion and oxidation (green stuff) with some fine sandpaper. Replugged the bulb and still had the same problem.
Swapped bulbs and the problem stayed on the right parking light. I then disconnected the socket and swapped sides with the left side. It now worked on the right side, but not the left side.
I would also recommend putting in new bulbs. They're cheap.