Cracked cooktop, faulty control

About three months ago, the glass surface cooktop started to develop cracks similar to what happens to a car windshield. About a month ago, the cracks turned into fault lines, making the glass surfaces unlevel and rendering the burner unusable. Also, the lower left burner dual control would not go to simmer after being on high. No information could be obtained about how to access the cooktop. I placed a service call to a local appliance repairer. For a service call fee of $54, he instructed me on how to pull the oven to access the cooktop, and quoted a price of about $725 to replace the glass surface and defective control. For about $350 in parts and about 3 hours labor, I replaced the glass and control, and banished a terrible buzzing noise the oven was making during preheat and baking.