Bob;
My FSM shows NO gasket on the strainer, But the '89' parts book I have (Dodge) shows 2 gaskets #MD609 040 and the screen #MD609 041. There is a gasket between the screen and Spacer and the spacer and valve body.
This is '89' model year. I'm not sure if others will be the same.
Always start with a fluid flush, and go from there.
Best of luck
Kary

1987 Mitsubishi Pajero "Modified"
The other original Mitsu brother
Northwest Trailmaster