Jim,

There isn't a Service Bulletin number for the arking of the right or left turn signal sockets and bulbs. The replacement is covered under warranty. Earlier Abe C. posted about getting glass based bulbs instead of the plastic/composite base bulbs Volvo is using. The charring you noticed is caused by loose connection, the replacement bulbs (although the same style) have a wider base to help with better contact. Removing the bulb and moving the socket contacts closer to gether and adding some die-electric grease will help with the contact problem.