To be clear, you turn the one knob and gas should not flow until you push it in, and it shouldn't keep burning until the flame has heated the thermocouple.
If I were working on it, I would start by removing it so I could work outside, then soapy water to find what is leaking. Valves use grease which dries out, could be a corroded line, loose fitting...
Some of these used a "zip tube" to light- a tube from front to back with holes in it that gas came out while lighting- you basically had a small wall of flame running from front to back.
-- Chris Bryant