I've got a similar issue:

Recently purchased a 2004 SSB Coupe and the previous owner had put blue LEDs in the front turn signal locations. Both worked as turn signals, both worked when used as turn signals. Other than the fact they looked dorky and were highly illegal, everything worked as it should. Well, other than that crazy fast turn signal thing, but I put that down to a lack of resistors and the fact that these cars don't seem to like LEDs on outside lights. Fine.

I pulled them out and replaced them with standard orange turn signal bulbs. But I also pulled both headlight assemblies completely out of the car as they needed a full sanding and re-coating. I put everything back in and ....... no turn signal on the right side. As with Chiminoul, if I pull out the socket assembly from the right side and swap it with the left, it works over there but I still have no right turn signal. Rear signals are confirmed to be working as are all other external lights. I do get the "light out" warning light on the dash. I will also admit that the main connection on the right side headlight assembly was a bit resistant to removal, but installation felt totally normal.

I'm thinking I might have damaged something when pulling that connector out and that's causing the right side turn signal to not get a..... well.... signal. No free flow of electrons as neeeded, when needed, so to speak.

Thoughts???