Pilot light but won't stay lit

I have a Majestic, direct vent, gas log fireplace model DV360 that is 16 years old. When I try to light it, the pilot usually lights quickly and will stay lit as long as I am pushing in on the pilot knob. I have tried holding the button anywhere between 1 to 5 minutes. I also took a lighter to the TH and TP to try and make them hotter. The problem is, the second I release the pushed-in pilot knob, so that I can turn it to ON, the flame goes out. I have tried cleaning the thermocouple and thermopile and blowing out the pilot the best I can. I can't see the burner tube because I believe it is hidden under a burner plate/burner housing assembly, so I can't clean that. The pilot is a nice blue and shoots out in three directions. It just that the pilot won't stay lit long enough so that I can turn the knob to ON. I also have a wall switch that I normally don't turn on until after the pilot stays lit on its own but I tried turning it on while trying to light the pilot but it did help any. The TH, TP and Pilot look to be clean and not at all corroded. Funny thing is, it was working fine for the last month and then stopped lighting. Any suggestions on what to try next.