What I discovered in my case is that the problem is due to poor design. The metal posts that come out of the stove are U shaped or half circle with the opening facing upwards. The knobs then slide on to the metal posts. However, once the knobs are installed, there is a gap between the stove face and the back of the knob leaving the metal U shaped post partially exposed. Any cooking liquid such as bacon grease, oil etc has the potential of dripping between the stove face and the knob. If the grease lands on the U shaped metal posts, it acts as a channel and the grease runs down the metal shaft into the valve inside the stove. And let me tell you, it's like cement if it dont catch it. If you can't free it with a degreaser, you'll need to buy a new valve. ($30-$40). Each burner/knob has it's own valve. To access the valve you have to remove the top of the stove, then the front. Don't forget to turn off the gas.
What they should have done is designed the posts so the open side faces down. This way it doesn't act as a funnel for grease and debris to enter the valve. Just poor design.
