The secondary filter is messy to change, park the car on the lawn. Unscrew the bolt in the center of the canister and the canister comes apart. The old filters were made of felt like material and the secondary is the finest filter.
There are actually 3 filters: the pick-up screen in the tank, the "primary" and the secondary.
If I was doing this, I'd drain the fuel tank, and remove the pick-up screen from the tank to make sure that it was clean.

Since the car sat for 3 years change the oil and filter too.

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Over 21 years I owned several:
w108
w110
w111
w115
w116
w123
w124
w126
w212