Oven will not stay lit?

The right hand oven on my lesuire cookmaster will not stay lit once lit.im pretty sure it is the button not sticking in as I hit the button once and it stuck in and stayed lit but now it will not stay lit, I tried spraying it with wd40 but this didnt solve it. Has anyone else had this problem and if you have what fixed it? It s an old cooker but probably something simple to fix it