The average price of a gallon of self-serve regular gasoline in Los Angeles County dropped Friday for the 38th time in 39 days, decreasing nine-tenths of a cent to $5.404, its lowest amount since March 11. The average price has dropped 76.2 cents over the past 39 days, including 1.2 cents Thursday, according to figures from the AAA and Oil Price Information Service. It decreased 27 consecutive days, was unchanged June 22 and resumed the followin…