judging from the way it looks and the p/n, i'd say it's a PG7 filter which would require the cleaning I just gave mine.
I have updated the top post... have a look.
Hey splat, I never thought of the simple green idea... have you ever followed that cleaning up with a spray type cleaning to see what was left behind? I'm almost tempted to do a 4th cleaning on my filter but I'm running out of time... doggie needs his run and I have to go to the geek store (Fry's electronics) before traffic starts piling up...