V6 2WD and 61000 miles. First it was Check Gas Cap light. Then a little later, check engine light. Went to service place, said to get a new gas cap. Said that's all it was. He reset the codes to go off. Got the cap, passed the emissions test and days later, both lights on again. Mazda dealer charges $100 to read the codes. Do I have to get a certified MAZDA gas cap rather than generic?