Call Sac sky ranch... they have parts for the strainers.. such as O rings... and no the washer does not have to be changed... if it is inspected and found to be in good shape... only the O rings need to be replaced when you take it apart...
the screen and plunger can be gotten at McFarlane 800-544-8594...
http://www.mcfarlane-aviation.com/ as well as several others are making them now out of SS which is less corrosive and seems to last longer... but, the original is lighter and stronger for its weight... you and your mechanic have to make that decision...
They have other items that will sub for cessna parts...
As to the replacement of the screen and gasket... under it... we want you to look at the filler pipe... the alu pipe that hangs down thru the brass screen... as we showed on the pictures which were posted on the other web site... if the screen looks clean and clear... then their is no reason to take it apart... the other O rings up in the plunger area... are also common ones... and run about a buck each...
Hope this helps... you all might want to get a few of the larger O rings... and the ones that go under the nut that holds the cup on... those two are the most common ones used... and come in a sealed paper package... but, watch the cure date on them.. nothing over 5 years....
HOpe this helps .. GMAs...