X2 on the dirty pilot light orifice. Can be carboned up making the pilot flame smaller. If the flame gets too small, the change in draft when the main flame goes out (or opening the door to check progress while the main burner is in it's off state) can be enough to blow out the pilot (listen close and you'll hear a "woomph" or "pop" both when the main burner comes on or off). A starting point would be to pull the pilot assembly out and eyeball it closely. Don't try to make it bigger, just be sure it is clean. Also, like mentioned above, be sure the thermocouple is centered in the pilot flame. It has to be hot enough to expand the internal fluid so it can push the pin out that holds the pilot valve open. There is the possibility of the internal filter in the gas control valve has gotten stopped up but those are pretty big compared to the amount of gas that passes through them so that's not likely. I imagine they do get replaced but I've never encountered that, even on 30 year old stuff.
