It is most likely your turn signal socket in your left headlight. Either it is damaged or one of the contacts in the headlight is damaged from not making good contact. Take out the socket and inspect both contacts if they are fine then be very careful and move them outward a tiny bit. If that doesn't work then use a small mirror to inspect the contacts inside the headlight and you might see one of them has a hole. Then the hole can be repaired with solder but the headlight must be removed. (not a fun job)

If your turn signal socket is damaged then you can order one on eBay from an overseas seller. This has been discussed on the forum and you can search for the links.