Appliance Guys:
I have a Frigidaire Gas Oven, bought in 2005. It has worked fine, until a month ago. The 4 burners on top are fine. The Oven/Broiler long flame bar, a couple months back, started to take 3-5 minutes, before it would light, I smelled a little gas. So after it DID light, I bent down with the broiler door open, and the flame looked Ok at first, nice and big.

But as weeks went on, it took longer to light. I had to light it, I had food all prepared, so just to try something, I tapped the pipe in back, near the air vent hole, with a Plastic rod, and THAT made it light.
But NOW, even if I can get it lit, the flame is smaller, I have to turn it on FULL (Broil), and after 15-20 minutes, it dies out. Once it dies out, it's almost impossible to light again.
I am an Electro-Mechanic tech, pretty handy. I can fix almost anything I've ever tried, machinery. Can someone give me some help, likely causes, faulty parts? I 'd REALLY appreciate it.

First, I want to say Thank You, very much, for responding. I'm not sure where the flame diffuser is, I would guess the pipe with the holes, but I'll get a blow-up digram, to make sure.
But I just wanted to ask, would the "flame diffuser" have cause a Full Flame, with difficult lighting one or two months ago? Becuse the Original problem , and still the biggest, is it not lighting at ALL. And after about a month, the "difficult lighting" became MORE difficult, with a weaker flame.

Do I remove the flame diffuser from the oven, and scrub it?