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Cleaned it with air from the inside out, then washed it by hand with dish soap and let it dry. Do you oil it? I don't remember it being oiled when it was new.
I believe you are supposed to spray it with WD-40. Seriously.
As per their website:
Cleaning the filter
Any after market filter cleaning kit will work
If you choose not to use an aftermarket cleaning kit, wash using warm water from the back side of
the filter
Use a liquid detergent, lather filter very well and the rinse again from backside of filter
You may dry filter with hair dryer, or let dry naturally
Once dry re-oil filter with any aftermarket filter oil or we prefer WD-40