I was cleaning my stainless steel range a few months ago with a cleaning paste( vinegar and baking soda) and right after I cleaned it two of the burner valves would not turn, even with pliers. The two other burners work fine and all burners are getting a spark. I'm guessing that the cleaner got into an area it wasn't supposed to and clogged the other valves. The repairman wants $300 to buy two new valves, two knobs that were stripped and labor. Can't I just clean the valves if I can get to them or do I have to buy new ones when they become clogged. Thanks for any help.