How often should we change the fuel filter?

On the newer cars, it depends on what the manual says. Personally I change mine every 100,000 miles if it hasn't already been changed for some other reason. That'* on my car where I know it gets halfway decent gas most of the time. On other people'* cars I'll generally use 50,000 miles as a rule of thumb.

On the older cars, especially with the filter in the carburetor, I'll change every 25,000 miles or sooner if I'm suspicious of it.

That having been said, I've never had one plugged up in any of my cars, but somehow I've run across a bunch in others' cars that have been. I don't know what kind of swill they fill them with, but I'm glad I have some kind of standards.

Pk Ave owners manual does not mention replacement mileage anywhere. However the dealer recommended part GF578.
I just noticed the Owners manual states GF627 Huh? Going to have to call the dealer back & see what'* up.
It'* been 6 years since I last changed the fuel filter & about 60 k miles.

Dealer using my VIN # confirms box # is GF578 or part # 25121293. The Buick'* owners manual is obviously an outdated part. All good!

When I bought my Park Ave 5 yrs ago it was extremely dusty and dirty. I mean, they had cleaned the car but in all the hidden spots like the gas filler area, door jams, etc, I could see a lot of dirt. there was also gravel everywhere in the frame.
So anyway I always tune up a car when I get one, even though the car ran good.
When I took the gas filter off, brown crap came out of the inlet side, and I mean a lot! So I cut it open and it was almost black. Car had 250,000 on it when I bought it so who knows if it was from the filter not being changed or dust getting into the gas tank. BTW this car came from South Dakota. Looked like it lived on a gravel road! Everytime I would wash it dirty water would run out of the deck lid where it closes, I finally took off the inside carpet like cover on the under side of the lid and it looked like a dust storm had settled in there.LOL. cleaned it and the dirty water stopped.

Dang, sounds like the fuel filter had never been changed!
By chance did you get a photo of the inside of the filter?

unfortunately I didn't get a picture of the filter. the odd thing is, the guy I bought it off of said he always took it to a dealer for service and the way the car runs I believe him. I guess they just missed the fuel filter or maybe it got so dirty from a dirt road? Who knows.

Many would no know to use a good ethanol stabilizer like StraBrtite Star Tron. It makes fuel good for 2 years.