My husband drives a GMC 1500 Sierra. It has about 120,000 miles on it. Last year, the turn signal all of a sudden started flashing fast. He replaced the circuit board (I think that was what it was called) in the taillight. After that it worked just fine...til last month. It went out again. Replaced it again, worked fine. Last weekend, it started doing it again, but only like every other day. Any ideas?