yeah, there is a plate between the filter and block. It has a gasket and a plastic washer.
If you look inside of the threaded fitting that the filter is threaded on, you will see a square opening. It is 3/8 inch to fit your 3/8 ratchet extension. usually you will need a 3/8 nreaker bar to remove it. this loosens the adapter plate which has the gasket under it. the plastic washer goes in the middle (I believe) between the plate and the block also.
(although I am not 100% sure it might go in between the threaded adaptor and the plate. anyway, when you take it apart you will see where the gasket goes and the plastic washer. these gaskets and seal are commonly found in the engine rebuilding gasket kit.